For pure protection, I think 2 layers is plenty. Even 1 layer should be enough, as quite often, harsher cleaners are needed on wheels, so it would strip the SG.
I wouldn't top with carnauba, as that's really just for looks, but if that floats your boat, go for it.....
If you clean your wheels and they are in decent shape then SG should be all you need. What you are trying to do is seal the clearcoat againt brake dust.