You could probably use a 90 with a divider until full grown and then a 120 would probably be ok. Obviously, the larger the better.
You will NOT want to stick your hand anywhere near the male when they breed. He will attack you and being a guapote, it WILL hurt as they have pseudocanines. I've even seen them jump out of the water at a friends hand when he was opening the lid. They will also bang the tank glass to get at you, so don't tease him. This sometimes causes a loss of teeth but will grow back in a few weeks.