Hi, sorry for delay, am now back from holidays, so can look a bit more.
So let's take it step by step, because I think a lot of what you want exist already :
In Custom Games (as opposed to Play now / Play scenario), You can choose the amount of total players in a game anyway, regardless of the size of the map. This can be up to 18 players (you can code more in C++). So you can have 2 players on a huge map, or 18 players on a duel map. No restriction.
The actual size of the map might not depend on what you choose on "size" in the Settings of the game. Maps like Inland Size change size with this option. Earth Evolution (and presumably Vadus_World) have a fix amount of tiles in all cases.
You CAN play with american Civs on EarthEvolution, there are starting locations for those (and I've added more on EarthEvolution4 for new Civs in case, feel free to donwload in what I linked to you above).
So if you expand the amount of Played Civilization to 18, and you select them to be American Civs (amongst others), I think almost all your request are answered ?
Also, in EE4, I've added a few different combination of 18 startings spots. So you can shuffle through different preselected list (and I can do a new version with more specific combinations if you wish).
Try all this and let me know if it suits ? If all this works, you can just use the 2 mapscripts (EE4 + Vadus_World) ? I could code a map that let you select between the 2 logic/scripts, but I think much easier and cleaner to just have 2 scripts?
