Year 3
1 Heron carrier (flag)
3 Captained escorts (Shrike, Centurion, Afflictor)
4 Wolf frigates
4 Shepherd drone tenders (because A. they have salvage platforms, and B. anything slow as a Salvage Rig at combat speed 50, gets caught by pirates)
8 Combat Freighters of various types (Wayfarer, Hound, Cerberus)
5 Dram tankers
This fleet runs out of fuel, runs out of supplies, and even when it doesn't, spends all that 485,144 credits emptying out multiple planets for supplies and fuel. (When even Chicomoztoc doesn't have enough supplies for you, you might just be overdoing it. Just a bit.)
Doesn't seem like a bad fleet. It might be that you're still paying "full price" for the upkeep on them.
The only thing I'd suggest changing is leaving your carrier(s) inder AI control, and picking a combat flagship that suits your taste so you can more effectively pressure or run interference. Or take advantage of openings.
That's a personal choice though. Do whatever you're happiest with.
First thing to consider for getting that maintenance down is finding the spec for the Efficiency Overhaul mod, and fitting that to everything in your fleet.
This will reduce your supply upkeep and fuel usage, reduce your minimum crew requirements, and increase the rate at which ships recover combat readiness.
The next thing to do is look in your character skills. On the green Leadership row, there is a Fleet Logistics skill which reduces the supply upkeep for your entire fleet.
On the blue Technology row there is a Navigation skill which reduces the rate your fleet burns fuel.
You want both of these.
You'll need 4 skill points for Logistics. And 6 for Navigation.
The next bit requires a bit of divergence from "normal", and costs a non-trivial amount of skill points. And only works if your ships are damaged and have (D) mods.
Firstly you will need to spend 3 skill points on opening up the yellow Industry skills to maximum.
And then put another 3 skills into Safety Procedures, which cuts all the negative effects of (D) mods in half. (Also allows you to Emergency Burn with no supply/readiness cost, which is really nice.)
Then another 3 points into Field Repairs. This is the biggie, it makes every (D) mod on every ship reduce the supply upkeep cost.
If you're still struggling for fuel, it may be worth putting
another 3 points into Recovery Operations to increase the amount of fuel you get from salvage by 50%.
Doing this, it is possible to accumulate so many supplies that you end up throwing them overboard due to not enough room.
The caveat to this, is that you need to lean fairly heavily into combat, and become confident enough to take on multiple fleets, sometimes back-to-back to get your supplies and fuel.
And don't forget to put bulkheads on everything or use damage control skills to make sure everything can be recovered, with more cost-saving (D) mods.
There's a neat skill tool
here if you want to see what the skills do outside the game.