I do not have the same setup, but I did have a 25mm spacer on stock 20 inch wheels with coilovers that ruined 2 of my front tires when cornering. I suggest 17mm spacers. I do not have spacers anymore with different wheels.
Ah yes, I am familiar with this area, grew up in Hilliard, but now has terrible traffic! If you see a LOUD 2015 black GT with gunmetal grey wheels, that's probably me haha
No special tune = 91 or 93
Flex Tune = 91 or 93 or E85 (Doesn't Matter)
E85 tune = E85 only (You can give or take a little ethanol does not have to be right at 85%)