Actually the cars getting bunched at the start of the race has to do with avoidance code. You see, the cars don't play well together due to UE4's collision, so we have them avoid each other until it's fixed.
As for widening the race start, I was thinking about widening the gate at one point. Still could
And regarding # of vehicles, we need to implement an opponent count. I don't see why we can't put 20 player starts in the level. Don't whine when all the dust effects send your PC into the stone age, though