ON TOPIC: If you want to make a good 4v4 map I recommend you to divide the map into several pieces,part open, part urban with garrisons and close range and part something like a forest (half open-half closed).
So like Lienne Forest? I feel like it does a good job at evenly mixing urban/rural/forest combat. The main problem I've been having (at least with my current map) is setting up European cities. They're so claustrophobic it's difficult to leave spacing for tanks and whatnot.
And do not overdo it with red cover, or Allied factions will hate you.
Why specifically Allied? I don't really like to use red cover anyway, I prefer a lot of yellow and a bit of green.
Last but not least, never place strong garrisons on important locations like cut-offs or fuel or middle VP, as it makes the game too campy and cancerous. Garrisons are fine, but only as long as there are many of them on unimportant locations.
This is one of the biggest questions I have. There's no doubt that buildings give an advantage early on with MGs and whatnot, but I feel like mid-late game they're more of a liability since all team games eventually devolve into an arty arms race. Should buildings near capture points be avoided?
For community maps with the most play and most downloads... you just put 1-2 chokes on the entire map and let people stomp AI. Balance won't really matter here as long as the map has lots of explosions.
Yeah, I've noticed the top maps in the Community Modding Hub are things like Lyon, Sittard Summer, Achelous River, etc. However, I'm not to keen on "bridge maps" for PvP ever since our group did a 4 v 4 on Achelous River. It lasted for four hours and resulted in my team "losing" because literally nothing could get done and I had work the next morning.