Well, if you could set up the bindings on the buttons so that 4 buttons were modifiers (think shift key) & still have 6 buttons left to assign bindings too, you could certainly play with 30 active "abilities".
left stick - camera control
right stick - tooltip (mouse directional)
left trigger - forward
right trigger - jump
back - strafe left ~or~ camera in
start - strafe right ~or~ camera out
Your other bindings would be something like this ~button 1,2,3,4 the directional pad
Button A,B,X,Y, black, white
Button 1 + A,B,X,Y, black, white
Button 2 + A,B,X,Y, black, white
Button 3 + A,B,X,Y, black, white
Button 4 + A,B,X,Y, black, white
I can see that working out BETTER THAN fine with any of the 3 classes I've played to level 50. In fact ~ that's really all you need.
The game would be easier to play with a keyboard & mouse, but if you have to use a controller ~ I don't see that it couldn't be done. What would make it different ~ is you would have to pick between steering your toon & activating abilities. So you wouldn't be doing a whole lot of casting while moving.
Certain AC's and specs can get by with a LOT less ~ Gunnery Commando and Telekinetics Sage for examples. You could be a damn fine Commando or Sage healer with only 12 "hotkeyed" abilities. And neither really requires you to be mobile too much while casting in PvE.
You will have to leave off the out of combat stuff like, quick travels, speeders, pets, field mailboxes, class buff, etc. ~ but that won't impair your ability to play or even kick ***.