Hi JJ and welcome to Simply. I think a 120 works great for adult fish. If you are thinking of growing them out you might start them off in a 40 breeder and move them to the 120 as 4.5 to 5 inch sub-adults. I suggest that you do some research here on the forum. Lot's of good info here. As you read around you will get a feel for filtration and some of the other questions you might have. I see you found Al's video. That is a great starting point.
Pat