Alright!
I played a game and really enjoyed the mod. I already have some ideas/feedback which I'll leave here. First off, I want to start commenting the *Other* "First Playthrough Impressions" feedback post that was posted before mine (a few weeks ago). Without having to repeat what they've said, I want to agree with some pointers:
- The "added time" before being able to exploit certain resources can indeed be "troublesome", but manageable. I guess I had more time to do more scouting and such, which is nice, the one thing that really felt "too far away" was chopping rainforest;
- The barbarian ships are truly evil ... xD We maybe need an earlier ship (units expansion) on fishing since Sailing, being on the new era, has a very steep price - or have barbarian galleys only appear on the second era.

Now here's some feedback on the units changes (I *am* using all the unit expansions for the mod)
- Arquebusier: could perhaps cost 10 Niter? Would be consistent with the Scout Rider>Horseman idea of the "early" unit using half of the base resources; the musketman being the usual gunpowder melee unit, I think it would make sense for the arquebusier to require 10 Niter
- Dragoon could maybe start introducing the resource maintenance by costing 1 Niter per turn since it only requires Horses?
- The above logic could actually be applied for a lot of gunpowder-era units that do not require any niter, like Mounted Rifles, etc. At the same time, I understand the idea of not locking a player behind a certain resource, so I'm not sure what would be the best way to do this. I just felt like I had too many niter in my game :P
- Infantry and Howitzer requiring Oil feel a bit weird. infantry because we'll then see mechanized infantry (which makes more sense requiring Oil) and howitzer because the model still looks like a tugged vehicle (and we do get a SELF PROPELLED Howitzer, which only adds to the weirdness). I guess the oil (for infantry) could be justified by plastic, but I'd personally like to maybe see them using Niter or a mix (if possible) like Iron to build, Niter to maintain (that could also be applied to future stuff, giving a better value to iron towards the end of the game)
- Finally, the units with Uranium maintenance... I feel like there should be some uranium per turn costs, for balance, but maybe just energy and GDR? Because one of the biggest traits of nuclear reactors is how, well... how long their fuel last - and having to pay uranium every turn for each nuclear powered unit seems a bit... too much. I'd be fine with them having perhaps a larger uranium cost (and gold maintenance) but no uranium maintenance.
- About the "mixed" costs, they could be cool for a lot of things, like airplanes requiring aluminium to build and then oil per turn, etc. But then we'd have no use for aluminium (per turn) so I'll leave all that balance magic to you, these are just thoughts/ideas :)
- As unit suggestion, we could have an early air bomber (Alongside warplanes; it could be renamed "Air Warfare" and include an AIRSHIP! Bombing airships would be really cool!)

Also some feedback on tech tree locations and such:
- I had a mod that doesn't work with 6T and it was relatively simple but quite useful - "Earlier Canals". I think it could be cool to have that in the 6T tech tree too, because I always feel like canals are not that useful anymore when they finally arrive (due to how easy/well developed your harbor cities elsewhere already are); Maybe construction (like in the mod) is too early, but perhaps "Buttress" or even "Gunpowder" could be good compromise?
- I feel like Steel is very underwhelming now... Once a game changing tech (because of the fortifications upgrade), it's now there just to unlock Ruhr Valley - which is a pretty nice wonder but... that's it. This feels a bit "odd" because industrial steel is a real game changer IRL. I don't know what could be moved around... So here are some ideas: Perhaps some nice yield bonuses to factories/workshops, even nicer yield bonuses to iron mines? Not sure...

Sorry for the wall of text! 6T just injected new life into my game so - if anything - I just want to contribute with ideas and feedback!
Thank you for the wondrous work!