190L tank would probably be fine for the time being, I doubt you could house much else with them once they get breeding?
Yeah, I'd be stoked for a 10inch male; I think growth drops away more after 8 inches. I saw a 12inch specimen on MFK that was either 5 or 10 years old, its face was rather calcified.
Hybrid is probably at least double the cubans size and inherited anger management issues from the flowerhorn side of things, attractive fish though, and I can see solid teeth on it too. I think I'd be more comfortable trying it on with more cichlids in the tank so that aggression is spread out, I want to get a large oscar or 2 as I feel they make excellent dominant fish - might be more dangerous if the hybrid was top dog.