They'll get along with anything, just don't put them with something that will eat them Make sure theres loads of hiding places though, they're quite skittish but do get bolder over time. Tank size, not sure, I have 6 in a 15g with a few tetras and a juvie betta.
No less than a 10gallon, no more than 7 I would say and have lots of hiding places. They'll be more active then and feel more secure. You'll still rarely see them most likely however. Black Kuhlis I hear are more outgoing but I've never kept those.