Not going to reply in too much detail to most of this, it just makes Sense. Single driver, the worldmap selection, focusing on different Parts then the AI. It either makes Sense as explained, or makes Sense in that I just thought it was further along in development then it is, so I just thought there would be more. Like the AI i.e.
As for turning in Place for pathfinding reasons, can't you just increase the Turnspeed for various Units? So Tanks turn as slow as they do, while Infantry turns almost instantly? I'm assuming you've tested with your desired max Unit/Player count in a max sized map to find out that the Pathfinding needed workarounds like that to not lag out? I'd assume with a prebuild navmesh, it shouldn't take too long to just lookup the closest desired Points while already driving, but I don't know anything about your Architecture obviously.
What do you think about the build menu though? Currently we have three things displayed: 'things you can build', 'things you can't build because you don't have enough money', and 'things you can't build because you don't have the tech.' I'm thinking it might be better to hide all the 'things you can't build because of tech', since the tech tree is accessible in-game anyway.
Things you can't thanks to tech don't need to be there I think aswell. If People are confused, just put a tech tree lookup into the Game, and/or display a tooltip of Tank ( Requires Tank depot to build -> unlock by building (BuildingYouCanBuildRightNow) first). Something like that maybe. I'd also keep the other options, so things you can and can't build in the same place, and just grey them out, not swap them between menues. Makes it more clear I think.
Color selection order and default settings I think we could change into something a bit more 'gamey'. Does 'blue' for P1, 'red' for P2, 'green' for P3, and 'yellow' for P4 sound good?
Sure. In the End, it doesn't really matter all that much, but blue and red for Player/Enemy is rather common. Maybe just look at whatever Strategy Game you want, and copy their default color Layout or something.