I just checked the NSIS manual and it doesn't seem to have an easy option to download files during install so I will not implement that idea no matter how popular it is

Thanks for your input in the rest of the thread, I'll definitely consider changing / adding maps since there seems to be general consensus on it.
I think a set of good but not too often played maps would be best. Players will download the most popular maps anyway, and this could get the somewhat less known maps to be played a bit more. IMHO whether a map is good isn't entirely subjective. A map can have obvious problems like too much/few chokepoints, clear bugs, lack of metal/way too much metal (no offense lol), boring/repeating/non-tiling texture, etc.
I do not really like the idea of multiple installers etc., since more installers = more testing and more developing time.
Anyway, I'll come with a semi definitive suggestion regarding which maps to include sooner or later.