It all depends on the offset if you need spacers or not, not the width of the rim. I run 18x10 ET45 BBS wheels on my car, and its a perfect fit. Most of the Carerra wheels you see are ET65, which will require a giant 20mm spacer. Search carefully, you can find wheels that require no spacers for our cars.
As to the second part, I run a 265/35-18. A 285/30 fits, and one can argue looks better, but it will also enhance understeer.
Patrick
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