how about custom signs? not the original ones (thinking of Green Neon (non-animated) signs)

What's up with those?
Do you want to use them and are not sure if they are allowed? Sure they are allowed.

All signs are allowed, right?
(as long as they arent racist, sexist...)

The rules say nothing about forbidding signs. Of course all signs are allowed!

It's only after I finished my map that I realized something not explicitly described in the rules. The rules say that the car must switch sides at least three times, but for a multilap map, is it three times in total or three times per lap? (I went fully crazy and did 4 times per lap, so I think I am respecting the rules whatever the answer is...)

Yes, it is per lap.

Let me actually define the timelimit for a bit better for multilap, too:
All rules that apply to a normal track, apply to one lap of a multilap map.

one very last question:
I know that i finished my map but can i build 64*64? -> 2 32*32 quaters?

Ok, thanks for the clarification! 3 switches in total sounded too easy for a multilap map

It shouldn't really matter which base size you use fredair. The importance are the almost touching edges of the two quarters. Also the map has to be playable in the standard nadeo titles: (Stad or valley or canyon) and TM2 titlepack

So can i use a 64*64 map and build in two 32*32 quaters? That would be unfair, because I woud have 4x more place to build. The 64*64 map is playable. You should change the rules, because the differnce between the 2 Basemaps is too big.

(32^2*2=2,048 // 16^2*2= 512)