The easiest thing Tofu is to install Windows on a partition of your Macs HD using Boot camp. Won't cost you a thing (if you already have a copy of Windows) and will be much easier. They don't really make games for the macs. The port games to mac.
The problem with SketchUp is that the texturing capacities are VERY limited. I thing the best possibile route is to model in SketchUp and then texture using another software (maybe LithUnWrap).Because, sadly, SketchUp doesn't support UV coordinates.
I believe that already most of the subjects have been already thoroughly discussed. And with Wookiepedia. Answers to general questions are much easier to find.