I went through this very issue a few months back. I ended up calling the boys over at Wilwood directly and we came to the same conclusion of using the Civic tophat, and the (don't quote me on this, I need to go back to my notes to confirm) rest of the Miata kit with the superlite on the 12" (I think) rotor. The relocation bracket is the only obstacle to overcome, but the Civic bracket may work with minor relocation.
As for the wheels/tires... Those Rota's should treat you nice, and as you mentioned I've heard of and personally seen great success in the Konig Rewinds. To be honest, an ET+38 on a 15x7 is a very very tight fit to the fenders. It's pretty much a guarantee you'll be rolling the fender lip for clearance. If you did go with the extra 1/2 inch (15x8 as opposed to 15x7.5 or 15x7) IMO you're flirting with knuckle-rub. As for tire size, a 225/50 is substantially oversized (in diameter) to stock. A 215/45 or even 225/45 is a little closer to stock, but still oversized.
Good luck with whatever you do. This should be an interesting project indeed.
What suspension setup are you currently running?
Here's a shot (for what it's worth) (oh and please please please don't knock me on the car being soooo dirty) of my Konig's ET +38 15x7 with 205/50-15 Kumho VictorRacer V700's. I would have gone with their 7.5, but it's only available in ET +0 so there was NO way it'd fit and the tire would have looked stupid.

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