Regarding offset, stock is 9.5 et37 front..... and 10.5 et43 rear. I'm running 15 and 20mm spacers respectively, and I believe I have as close to "flush" as possible with no "poke".
The "equivalent" to that would be 9.5 et22, and 10.5 et23... let's call that your starting point.
I would NOT go with a full 0.9 difference in rolling diameter between the front to rear wheels. However, going down 0.9 rolling diameter on all 4 wheels isn't a big deal. The worst that will happen is that your speedo might be 2 or 3 mph off. Basically, negligible. If anything, it will raise the overall gear ratio a little bit, and help improve some low-end torque/acceleration that you lost by installing heavier wheels. That's exactly what I did. I would try to stay no more than 0.4 difference between front and rear rolling diameter though. I know you really want to run the PS4s, so my recommendation, based upon the tire sizes available, would be:
Front: 285/30/22 (28.8 rolling diameter), on a 10" wide wheel, with an et28
https://www.willtheyfit.com/index.ph...=10&offset2=28
Rear: 335/25/22 (28.6 rolling diameter), on a 12" wide wheel, with an et42
https://www.willtheyfit.com/index.ph...=12&offset2=42
My only question to all of this.... is "how high" of an et can you go on the rear.... before you start rubbing against the inner fender?
The answer? Is.... I have no idea. That is precisely why I didn't dictate to Vossen what I wanted my ETs at.... but rather let them use their expertise to determine the best fitment for me. I have no idea what those ETs will be until my wheels show up, but I trust Vossen isn't going to steer me wrong. I've seen pictures of my exact wheel sizes installed on an F15... and they didn't look "pokey" at all. In fact, if anything, I may even run a small spacer. Considering I'll be lowering my car a bit.... I may HAVE to run a small spacer in the rear., just because I'm running such a wide tire.
I've already done all these exact calculations on my wheels (22x10.5, 295/30/22 / 22x12, 335/25/22) that in order to get the "exact" same external "flush" appearance that I have now, the wheels would have to have ETs of 35 and 42 respectively. Now, I don't know what Vossen will set my ETs at until they arrive, but I can make an educated guess on how much "poke-age" they will have before I even install them, based on those numbers.
As a contrast, Dubsd runs a 22x10 et21, and a 22x11 et18.....That means, his wheels poke out 7.5mm more than mine in the front, and 8.5mm more in the rear.