You already have some scrolling set up... its a bit irregular from standard scrolling uses...
The biggest thing though is there are zero horizontal scrolling. Most generally its SHIFT+MOUSEWHEEL but its not. Please please add this.
But a suggestion is to move toward a standard scrolling control set up:
MOUSEWHEEL -> standard screen up/down control
SHIFT+MW -> horizontal left/right control
CTRL+MW -> zoom in/out control
This would be wonderful to add/change.
Also there are a few posts on here about fine tune scrolling I agree. A good idea for this could be something as simple as a slider that changes the degree of which is scrolled each type of scrolling. (Up/Down doesn't need it though). Make it a key command and/or a visible slider on the screen.