I'm one of the original organizers for Mahon, have made most of the tools and cooperated in making the strategies behind the largest power in PowerPlay by far, so take that into consideration when you read my answer.
If you want to do PowerPlay just to try it out on your own, don't bother. The documentation for the rules is borderlines non-existent, and you'll likely end up ripping your hair out trying to make sense of it on your own.
If you want to do PowerPlay just to get the modules, that's like saying you want to do trade, because one of the Engineers wants more Kamitra Cigars than you are allowed to buy. That's not "doing" anything, that's just completing a single task that seems a bit grindy.
To do PowerPlay "properly", you should first have a sense of belonging in the game. Not to a particular system, but to one of the four major groupings - Alliance, Empire, Federation, Independents. If you don't care, then I think you'll miss out on some of the best parts of what PowerPlay brings to the table. Once you know where your allegiance lies, you can start digging deeper. Obviously the easiest choice is if you support the Alliance, as there is only one power, and the hardest choices are with the Empire and Independents, as they have four each.
Get to know the community that is built up around the powers that you're interested in. These days the majority of activity happens on their Discord servers rather than the forums or reddit, but it shouldn't be too difficult to find them (just ask in the sub-forums or show up in their HQ in open and ask around.
The communities are what makes PowerPlay really interesting, but defining how obviously depends on the community.
Personally, I see PowerPlay as the only end-game feature in the game, even though I have been clamouring for improvements and changes not just to the rules and mechanics, but also to how FDev treats it, for years (literally). Since I'm a Mahon organizer, I'm going to be using that power as an example.
For Mahon to have become such a large power, and to have consistently been at a default surplus throughout PowerPlay's almost 3 year lifespan, we have had to learn how to master other things beyond just hauling goods from point A to point B.
We have 123 control systems, 122 of them have relevant fortification triggers. In order to reduce their workload, a power can manipulate the background simulation to their advantage, and Mahon has 93 reduced fortification triggers. That's more reduced triggers than any other power has even had control systems. In order to do that, we are currently doing BGS work across almost 1,700 systems (this is about 8.5% of populated space). Some of it is simply monitoring to ensure that we don't suddenly wake up to 0 reduced triggers, but there's always something to do. While there are player groups with far more players, I doubt you'll find one that has as big a "back yard" as we do. Also, the 1,700 systems are just in Mahon space. Since factions inside Mahon space can be in systems outside of Mahon space, we actually have to monitor all systems which have factions that exist inside Mahon space. This brings the total size of what we monitor and work on to about 3,000 systems, or about 15% of populated space.
Through PowerPlay we have been forced to become experts at BGS manipulation. Doing that means you have to pretty much be an expert in almost everything; trade, bounty hunting, piracy, murder, NPC combat, mining, exploration, running missions and I'm sure I've forgotten some stuff here.
Since the Alliance is relatively tiny (about 890 systems or 4.34% of populated systems are controlled by an Alliance faction, compared to 5,234 Empire systems which is the 2nd smallest grouping), we have had to learn how to get along with not just Alliance groups in Mahon space (which is difficult enough) but also a fairly large amount of Independent groups. In total there are 118 registered player factions/groups in Mahon space - 29 Alliance and 63 Independents (and 24 Federation and 2 Empire). We try our best to get along with the Independent and Alliance groups, to the extent that our fortification triggers allows it (Mahon can only use Corporate factions to lower fortification triggers, and Communism, Cooperative, Feudal and Patronage risks increasing them), and if you ever want to get past the notion that Elite is "just a game", imagine the amount of manure you have to wade through when player groups in Mahon space start having in-fights and drag us into it (or we accidentally drag ourselves into it).
Through PowerPlay we have been forced to become, if not experts, then at least experienced in diplomacy. I easily spent 200+ hours working diplomacy between player groups in this game, without even being logged into the game. That's more time than I've spent playing Metro: Last Light, Europa Universalis IV and Wolfenstein II combined!
And without working and coordinating with others, it is impossible to effectively manage a power. If the organized group or groups behind a power decides to leave PowerPlay altogether, I doubt any power would mange to have any useful systems left within 8 cycles, and it'd be pretty much impossible to bring it back to any kind of useful state afterwards. It'd actually be a fun mathematical exercise to be honest. Technically it could probably be done in two cycles, but that'd pretty much require the coordination of all other powers from the moment it happened.
Without a community and a sense of community and belonging around a power, it would inevitably end up failing. While PowerPlay has been mostly in a sort of stalemate for more than a year from Mahon's perspective, we've never really lost that sense of belonging. We've been explaining to our members that it's important for them to maintain at least rating 2 with Mahon every cycle, because we've been suffering from underhanded attacks for more than a year now, and consolidation votes are the best way to ward off those attacks (not that they have relented throughout this - on the contrary), and they have done so, even though there's no real incentive to do so. We chose to enter a shallow turmoil this cycle to ward off such an underhanded attack, and as a result we saw a lot of new and old faces showing up on our Discord server, asking how they could help. Some of them are old hands who have simply remained pledged without looking towards PowerPlay, but they saw that Mahon was in turmoil and their first instinct was to run towards the fire. That's the sense of community that keeps PowerPlay alive (and I'm sure other powers have similar stories), even when it seems like nothing is happening.
This sense of community is also why we are excellent places for new players to start out. You've just bought the game? Cool - do you want the quick road to billions, or do you want to take the slow route through every single ship and every single type of occupation you could possibly imagine? We've tried it all and we know it all (well, maybe not PvP for all powers), and regardless of your skill level and knowledge, we can always find something for you to do. Every little helps, and we know that if we help you out as you move from your Sidewinder through a thousand hours of gameplay doing everything imaginable under the sky, you will help us out when you have the chance and ability (read wallet and ship) to do so. Not that long ago (I think), Hudson and Grom's pledges threw about 30 billion credits down the drain for absolutely no personal gains whatsoever. Combined they delivered 4,000 Cutter loads of preparation merits to achieve something that not a single commander could point to and say "this is mine", and they did it because of that sense of community.
And if you ask anyone who's done PowerPlay on a "serious" level, they'll tell you that you don't do it for the money, because PowerPlay is a credit sink. Sure, PvP can be a credit sink as well, especially if you're losing 30+ million per rebuy, but if you're the best of the best of the best at PvP, you're not going to see a lot of rebuy screens, and you might even make money off of killing other players. I honestly believe that outside of someone at FDev digging through the code AND documentation to figure out every single rule, I am the authority on PowerPlay rules - I AM the best of the best of the best, and PowerPlay doesn't make me money. The only way PowerPlay can make you money is through combat (either combat expansions or undermining), and neither of those things are helpful to your power on a day to day basis - hauling fortification merits is how that's done. Combat is important, but it does not keep a power running.
You can either wait 30 minutes to pick up an allotment (a maximum of 50 at a time), or you can spend 10,000 credits per ton to fast track an allotment. In order to maintain rating 5 (where you get 50) you need to get a minimum of 5,334 merits every single cycle. We've already ruled out combat, so if you want to get these merits free, you now have to ensure that you are docked at 107 independent times each spaced at least 30 minutes about (that works out to 53.5 hours), and in a Cutter (the biggest hauling vessel), you then have to travel back and forth between a control system and your HQ every 15 of those 107 times. Or you can spend less time overall by making money on the side that you then spend pouring money down the drain. Sorry, I mean hauling fortification merits around your power's systems.
PowerPlay at its best is a team activity, one that has been running continuously for the last 25,000 hours, with players from all around the world, organized into loosely affiliated teams with an official leader that has never ever done anything to deserve the loyalty of their pledged supporters, yet are somehow able to rally them into spending hundreds of sleepless nights or taking hundreds of days off of work in order to be around and be helpful in the hours leading up to Thursday morning 07:00 UTZ when the PowerPlay cycle is supposed to tick over.
I have more than 5,000 hours logged in the game, and I've probably spent more than 1,000 hours when not logged in to the game doing things that are directly related to it, simply because of PowerPlay. Yes, I am obviously an outlier in this (at least I hope so for the sake of humanity), but in the end it boils down to one thing really - the community that we've helped build. Not just around Mahon, but around PowerPlay as a whole. It gets a lot of hate from people who think it should be removed, but those people are/were also the first to complain and whine when Li Yong-Rui suddenly loses a system where they were getting their 15% discount, or if ALD or Hudson loses their favourite bounty hunting grounds because suddenly the bounties don't pay out as well. PowerPlay forces the community around it to be experts at almost all things the game has to offer. So far the only things I can think of where this doesn't apply are PvP, CQC and alien races, but that's mostly because we haven't a clue what happens if Thargoids takes out the only port in a control system.
When I spend time with the organizers from other powers, talking about how to improve PowerPlay (outside of fixing all the damn bugs), almost all areas of the game come up because they impact PowerPlay. Open only for PowerPlay? Well, that could/should also be applied to CGs, and that brings up issues with regards to blockading stations by simply occupying the landing pads, and as such that needs to be tackled. Open only also requires tweaking all kinds of other underlying mechanics, but due to the expertise we've been forced to accrue to be successful organizers, we know that a lot of those tweaks have already been solved in seemingly unrelated cases. PowerPlay has a lot of bugs that haven't been fixed, and we notice where those are affecting things that aren't directly related to PowerPlay, because we see almost identical bugs in other areas of the game.
Yet we keep being ignored. Collectively we probably know more about the ins, outs, bugs and unintended consequences that this game has than any other sub-community for this game, but because PowerPlay is boring and gets no real participation, we are ignored as irrelevant. It makes sense, of course, because we've already paid for the game - me playing the game for 5,000 hours is not nearly as valuable as 50 players playing the game for 100 hours. However, it's also completely discounting the most valuable players in terms of knowing the game's ins and outs. Don't get me wrong - I'm probably fairly average in terms of my knowledge of things like actual BGS manipulation or exploration, but I don't need to be. "I" have people for that. My community has people that can answer almost any question relating to the game, and that's why it's such a shame that these communities are constantly ignored.