As someone who has 2000+ hours on XBox and just put Horizons on to an old PC commander, I loaded up the game with 10 million in the bank and an a-rated asp from 2016, also NO mats/data or engineers unlocked.
If by the time 3.0 drops you'll have quite a few modules to upgrade, you may want to unlock some of the engineers and get some modules to G5 beforehand so that you start with a new G4 format to be upgraded to G5. Grade 1 to Grade 5 on every module every time sounds horrific to me even if it is potentially easier (think multiple weapons/boosters/HRPs/SCBs per ship). Regardless, I'd say you want to unlock Farseer at least and get your FSD upgraded to make money beforehand.
Personally I'm now unlocking engineers to get their requirements out of the way, and to upgrade a fully G5 engineered combat ship.
Now the money. Get allied as quickly as possible with local factions. Look for decent paying missions when you're neutral which should be indicative of good paying missions once allied. Here's what I did:
Went to Gang Yun (medium pad) - fed rep system. Boom data between there and HIP 64706. No need to stack, you'll get 20 each way (maybe need to include Byggvi on return leg or mode switch at HIP). HIP station is 24k ls away so each boom data will give between 40k and 140k each (depending on materials/data rewards - lots of high grade mats). You'll get around 2-3m per return trip and 3-4 trips per hour (120-160 boom data missions).
Once allied, sightseeing missions are between 5m (mostly aimless) for single hop upto 28m for 4 hop (elite). At allied, I'd take the 7-14m one or two hop missions, or the 4 hop for 28m (1 hop ~90LY, 2nd ~160, 3rd and 4th upto 360LY). The 28m typically took just under an hour. The 7-14m 15-30 minutes. My ASP at the time could jump ~40-45LY with a loaded passenger cabin. Dolphin would be a good cheapish alternative though it's the cost of the A-rated modules not the hull. Remember LYR 15% discount for ships/modules. My ASP setup:
Class 6 passenger cabin
Class 5 fuel scoop
2G planetary vehicle (though usually scanned from the ship, so not required)
ADS+DSS (or ADS and a docking computer)
Size 3 shield
Size 3 cargo rack
Alternative to this depending on your ship is to check out the VIP 'Transport to' missions around some of the stations a large distance from jump in point. Downside is that number of cabins dictate number of missions and potential profit, you'll want a shield since passengers will fail mission on any hull damage (think slighting glance leaving station), you'll also need a cargo rack for those stupid commodities. Also prefers allied and elite rated missions, and watch out for the 'passenger may be wanted in multiple systems' which can be more frequent than not. Oh and it's BORING sitting in SC.
TL;DR boom data & fed rep until locally allied with all factions followed by sightseeing missions, or jump on the long distance from jump-in bandwagon. Gang Yun system will give easy rep and a decent payout whilst getting to allied, followed by a more than decent 20-30m per hour doing sightseeing tours. Doesn't have to be Gang Yun, I'm currently on the lookout for similar systems closer to the central bubble. My main criteria now has become 'does the system have an easyish way to get allied and does it offer decent 3-5m sightseeing missions at neutral/cordial reputation).
