I think the number of models is only limited by memory space. And a model don't need much. So, hundreds are possible but makes no sense.
I have currently 8 on the list, 6 in use:
2 different typhoon H
1 Typhoon H with waypoint hack
1 Q500
1 Simulator (UAV Pilot)
1 Blade 350QX
and the two predefined (default) models for H920 and H480. Those two I do not touch.
It is always a good idea to export and save the models.
br HE