I have about 35 right now, as feeders, however, they don't get eaten and get to eat etc before getting eaten. What size tank do you have? Alone, or kept in small numbers, I find they aren't nearly as interesting as when kept in larger groups. Anytime I purchase feeders, and I get 10, they aren't nearly as interesting as a group over 20-30..
I'm pretty sure they don't produce a ton of waste, I have my 35 in a 10g with an african clawed frog, (what eats them), and they seem like pretty clean fish. I would really recommend though, to do a bear bottom aquarium, no rocks or anything, really makes their color stand out and they look so much nicer.
If your really into them pick up a cheap 10-20g somewhere and get a bunch, very interesting and don't get any credit.