There isn't really one, but there's a limit on how many elements (vehicles, objects, etc) you can have in a server, which is 65 535 elements.
There is - the object limit is the same as Race, but the streamer is MUCH improved (and tbh could still do with a rewrite ). This means you'll find you can place much more objects than you could in Race. You'll still have the same amount of objects on-screen as race, but the streamer means it'll priorities closer ones first which is much more effective than race.
so...the streamer is build in the map editor? or do i have to add anything else?