Glamours is on a per item basis (so, rather than "this is how I appear" it's "this armor now looks like another piece." You can use any armor to glamour, so long as it's a lower level than the piece that will be worn, and can be equipped by your class (if you glamour a piece, then try to wear it on a class that can't wear what it appears as, it will appear as the item actually being worn instead.)