Definitely use an A-rated power plant. The superior heat dissipation alone is the main reason to do this. With
Strix (my Asp X), with an A-rated power plant, I can start charging my FSD while still scooping - so long as the star has turned from red to yellow, I won't go above 90% heat. With a D-rated power plant, I'd probably hit above 90% just while scooping.
This heat dissipation starts a virtuous cycle all through your ship. With excellent heat dissipation, there will be many situations which you will no longer need to fire a heat sink, reducing your need to carry launchers. Likewise, you'll reduce the number of situations in which you'll take module damage, which eliminates most of the need to take a second AFMU.
Speaking of which, I've found that explorers tend to make big mistakes in their first 50,000 light years or so, and after that they settle into a travel/exploration routine that is predictably safe. I definitely saw this in my experience. I took a lot of needless damage in my first 50 kly, while my latest trip (~110 kly) saw me end the trip at 100% hull and almost no module damage. I don't carry two AFMUs, and I've never regretted it. With AFMU reloads, I just carry a small 3A AFMU, and then a large 5E cargo bay. The cargo bay doesn't normally hurt my range, but it provides some flexibility without having to refit (I can decide to salvage data caches and bring them back, I can fly with someone else and act as a light cargo carrier, etc).
Now, I do run a 3A power plant instead of a 2A. Technically I could depower my SRV hangar bay and go with the 2A (I did this during DWE), but I started getting paranoid. It seems reasonable that you'd have to have power for thrusters, FSD, and hangar bay in order to dismiss your ship from your SRV, recall it, and then re-board it. I'm not
expecting FDev to change the way they do power, but I don't want to be caught out in the middle of nowhere when some update changes that. I fully understand that it doesn't make a lot of sense, but we've all got our own particular brand of space madness.
I'm also a big proponent of avoiding the grind. When engineering first came around, I spent about an hour getting a 45% roll on my FSD and calling it good. About 200 kly later, I got an itch to do more engineering, so I returned to the bubble and spent a few weeks doing the rest of the engineering you see on my ship loadout above. At the time, it was kinda relaxing, because it was a nice break from my normal routine. I stopped when it got to be a bore, despite the fact that I technically could squeeze a little more performance out of the ship with a lot more engineering. We play ED to relax, and for me exploring is a lot more relaxing than grinding. My biggest performance boost was that single reasonable 45% FSD roll. One hour turned my ship from a 34 ly Asp to a 49 ly Asp. A few hours, during my second bout with engineering, turned it into a 51 ly Asp, which is a substantial gain even still. The rest of those couple of weeks gave me a little more shields, armor, and speed, and boosted my jump range by about half a light year. It's very much a game of diminishing returns. I'm sure I could spend another few weeks to do things like get a lightweight heatsink, G5 lightweight sensors, etc, but I'd probably only gain a couple tenths of a ly out of that, which isn't worth it to me.
Lastly: guns. I've gone back and forth on this. My first exploration Cobra was reasonably well shielded and fully armed, but now I'm flying a completely unarmed Asp with paper-thin shields, and I don't plan on changing that. My rationale? If I carry no weapons, then my only option is to run from danger. I won't try to fight with what is basically an extremely substandard gunboat. I'll run. And I'll run very
quickly because I don't have guns slowing me down. I'm an explorer. I'm out there in the unknown. If I run into hostile aliens, then the best thing I can do is survive to gather information on them, and my best chance of survival is to not pick a fight with them.