Well I once had my 10 gallon tank stocked with (it has changed a few times):
-a male betta and 3 otos
-3 male guppies and 2 male platies(no babies!)
-and 3 male bettas (it was divided)

If you want all male guppies they will get along, mine did and they did when I had 7 male guppies in my 20 gallon. You could also do a female betta sorority but it is alot of work making it work because they can be aggresive. My fav fish site and forum is www.petfish.net Good luck!