Oliver Knott has a group of them living together...not sure on tank size though. In fact, he has babies that are 52+ days old now.I think you could probably do more than one in the 65 if it's well planted, esp. since they explore all levels. I'm not sure the 33 would be enough for more than 1. They aren't total slugs but they're not spazzy like SAPs. They like to hunt around and stalk snails/look for food so it's a nice activity level IMO.
They will come to the front of the tank anytime you're near though! There is someone on here that keeps 3... Lemme see if I can find and tag them.