I've seen your C# Nocturne as well. I must commend you for the effort. Cheers.
I think you shouldn't worry about the limited dynamics yet, at least not before you got the bench problem straightened out. Believe me, a better seat and playing would be a lot easier. But you have to get used to it.
In my (short as of yet) experience, it's better to have a chair a bit too low than too high. Glenn Gould can play with an extremely low chair, but I've never seen someone play with an extremely high one like yours before. So pick up a lower chair around the house. Even if you have to drag the sofa in LOL!
