You can probable map the two functions to the same key.
Nope. If you have two functions mapped to the same key (you can tell because the conflicting functions are red instead of yellow), it won't even let you exit the config screen (just tested that right now).
At anyway, crouching *may* help your sneaking. It's hard to tell since sneak seems to be automatically checked at all times, and can succeed even when walking. But I think there's a better possibility of it working if you're actually holding down your "sneak" key (which I have mapped to ctrl, to keep it close to WASD).