You don't say where the fret buzz is occurring; if it's along the whole neck for a string then generally the action is too low; if it buzzes nearer the nut you have too little relief; if it buzzes up nearer the dusty end then you have too much relief. So, first off I'd say check what relief you have and adjust if needed. Next you need to check the nut slot heights, they might well be too shallow so that's compromising your set-up and I think often basses come with poorly cut nut slots. Only then can you adjust the saddles to achieve the action you're after and string heights will depend on the fingerboard radius. Fender offer a good set-up guide here http://www.fender.com/en-GB/support/articles/bass-guitar-setup-guide/