You could fit 2 Severum in there with my list, just a heads up. I think you've got the room.
Personally, with a 5x2x2 I'd get 3 Severum, 1 BA, 1GT, and a say 4-5 Arachthys Heckelii or some other type of Geo around the 10" mark like Surinamensis. Or if you were to go for the central mix, you're pretty much on the ball with what I would get, except it would be 3 Firemouth and 2 Severum, and take the BA out. I'm a weird numbers guy.
Personally, with a 5x2x2 I'd get 3 Severum, 1 BA, 1GT, and a say 4-5 Arachthys Heckelii or some other type of Geo around the 10" mark like Surinamensis. Or if you were to go for the central mix, you're pretty much on the ball with what I would get, except it would be 3 Firemouth and 2 Severum, and take the BA out. I'm a weird numbers guy.