I got them as 1/2" about a year ago...now they're 2 - 2.5".
I think the key to managing aggression with them is to give them plenty of caves. The rubber-banded-together PVC works great (and makes catching them easy too).
There are 5 or 6 of them in a 2'x2'x1' tank (which is like 34g). Lot's of floor space.
I keep them fairly cool (68-72 or so in the winter and probably 76-78 or so in the summer) and house them with some chanchitos. I know when a pair has bred because the rest of the fish are on the other side of the tank...and the breeding pair has turned color.