They dont get nearly as big as some of their cousins, average in the 5 to 6" range. I do believe peathenster has an 8" but that is rare! They are not very aggressive. They will chase each other but nothing major.
Getting a group is definitely a good idea. They are supposed to be more comfortable that way, which is hard to prove, but it definitely spreads out the aggression. Maybe I should start breeding them again....