well...what size do you want? You can use anything from 13s to 20s.
width and back space will vary depending on the wheel you choose.
Decide on the rim diameter first, then the rim width.

From what I understand, some people have run a 10" wide rim in the rear but that would be the absolute max on the rear with out frame mods.

I personally run 15X6 frnt (3.5 BS) 15X8 rear (4"BS)
16s, I would suggest 16X8 w/ 4"BS

Hopefully some of the 17" rim guys will chime in.