A neck shim WILL NOT help with fret buzz. A shim is only needed if you can't set the action as low (or high) as you like it within the travel of the bridge studs.
Follow the setup instructions on Rich's site, if you like really low action (less than about 2 mm) you'll have to make the neck a little straighter than Rich suggests for a "normal" setup.
Remember, about 2 mm is as low as can be exected with no, or little, buzzing. Lower than that and even an almost perfect fret level is going to buzz in some areas of the neck, if not the WHOLE neck.
Some buzzing is unavoidable, it's wood, it changes with weather/time, that's why every guitar isn't able to be set up exactly the same to begin with.
As far as nut hight . . . what I do is press the string right in front of the 2nd fret, there should be just enough space between the string and the first fret so that it's not touching. This will USUALLY give you the proper clearance for no buzzing on the open string and easy action.
All guitars are different though, so basic rule of thumb is this, the nut can be as low as possible just so long as it doesn't buzz when you play the open string.
Usually Ibanez guitars are shipped with too high a nut, but they are usually shimmed, so you can just take shims out.
No, you don't have to remove the bridge to remove the shims . . . again, go to Rich's site, it's all there, I'm not going to type again what Rich has already spent so much time typing out for you/us. :-)