Great thread, thanks for sharing. I think you mentioned going with 305s all around?
Keep in mind that if you are going with 305s, the new wheel width/clearance doesn't matter as much because the new tire gains width more than the wheel. Going from 285 to 305 is 20mm more width where as the wheel change is as you stated, only 1/2" (12.7mm). On the Gen5, the tire to strut clearance is more of a concern than the wheel to strut.
But of all this may be a moot point anyway, because the camber plates help a bunch.
Here is a calculator that I use,
https://www.rimsntires.com/specspro.jsp
