First off, I personally I wouldn't add guppies to a tank unless it is already cycled or heavily planted. IME gups will die as soon as ammonia spikes (those that survive will die when your nitrites spike).
I would add 3 gups max on a 10g aquarium. As for the sex, you can stick with all males if you don't want to breed and have to setup other tanks. If you plan to breed and have separate tanks ready, go with 1 male and 2 females. How you handle them when the females get pregnant is up to you.
Lastly, I don't know the quality of the gups you can find locally, but if you find ones that you like, get them. I personally will only buy from show guppy breeders because I have high standards for my gups (and the fact that LFS gups here are unhealthy and not-so-pretty).
Breeders? You can check this page:
http://www.guppies.com/forums/showthread.php/list-breeders-14286.html I personally recommend Frank Schwab
www.guppyalternative.com -- very nice guy with very beautiful guppies. He even let me drive to his house (1 hour drive) and see his guppy breeding rooms.
Lastly, you might as well read around the guppy forums. The forum isn't as active as this one, but a lot of good info can be found there, and the few members that are active are always helpful.
Hope that helps!
EDIT: I have had guppies since I was a little kid, but I do not consider myself a guppy expert, so if I gave a bad advice, I apologize in advanced
