1. I think that this means that it is currently in equalibrium, ie not moving at the moment.
3. Smooth disc would equal no friction, so remove the friction from you equation and see what happens, could mean it moves up/down the disc?
Sorry I can't answer 2, have had no experience with centripetal forces, from what I can see question 1 and 3 are just basic mechanics.
Hope this helps a bit