100 per player at the same time (the stack goes from 99 to 0).
If some of the floating texts are not to be displayed to all players, you may want to create them locally (using if GetLocalPlayer()==YourPlayer then
or whatever). They won't mess up with the handle stack since they use a separated ID stack, but that means you shouldn't use their IDs in hashtables for instance.
If you only show/hide floating texts instead of creating them locally, it will do strictly 100 at the same time.