They're not one of the really aggressive cichlids, but they can be while they're breeding. They'll eat small fish, but don't show much aggression once they've worked out their pecking order.
The can grow to be around 8 inches, and I'd recommend a 55 gallon tank for a pair, more for the room to move than the quantity of water. You could probably have one in a 40 gallon but that would be pretty tight. They like slightly soft water, with neutral or maybe slightly lower pH, but they're not overly sensitive to water conditions.
I like to keep them in pairs, but in my experience they've been fine in any number.
zombie threads. lol. We all do this when we start. Try looking at 'new posts'. You can post in an old thread, if its relevant. The aren't locked. But you are more likely to get a response to a new thread.