We've had up to five, and that went pretty well. The girls (2) pretty much kept to themselves in their own little sleeping spaces; the boys (3) tended to sleep in a clump together.
As you alluded to, the primary disruption in the balance came when there were outside cats trooping through... we had to resort to temporary "kitty valium" for one of the boys. The outsider moved on, and all was well again. L-Tryptophan is a really good idea... gonna remember that one.
Happy Caturday!
=^..^=
Your urinary stress diet contains it. It's good stuff to have around