For the axis mods, go with at least 225/35/18 because 215/35 is way too thin. Although, like others said 18x8 may be too wide even w/a lower profile tire.

And with the c5s, I'd just go with the 225/40/18, unless you're really worried about rubbing try 215/40/18.

Btw, wheelmax doesn't sell axis or RH wheels anymore.