Exactly what Zippy said. Absolutely no males with other males, and absolutely no males with females.
There have been many people very successful with housing females together, and I'll be doing so in less than two weeks.
Basically, 4-6 females can fit in a ten gallon, but don't expect them all to get along... and you'll probably have to take a female out to have her housed by herself if she is too aggressive. You must have many, many hiding places, so the less-dominant females can hide when other females are picking on them.
Good luck!