I don't know what swift springs you bought, but they're probably the Spec-Rs meant for fixed struts
If you are getting Fortunes, you want the swifts they provide as they are the correct length for their coilovers.
I think the radial mounts only apply to the fronts. The divorced setup in the back requires something different; fortunately, swift has the solution:
Swift thrust washers available from SPL
https://www.splparts.com/products/sw...t-washers.html
They are basically thin plastic rings that go between the spring and the mounting surfaces so they can rotate with less friction. this is what creates the "squeaking" and "popping" sound that occurs with coilovers during compression. One set should handle the rears fine. They are insanely easy to install, you're just putting one set on top of the spring and one set on the bottom. The radial mounts are just a fancier solution for the fronts.
you might as well get the adjustment extender to make life easiest in the future, even if you aren't doing a ton of adjusting
Stick with the fortunes. They are USA-rebuildable, offer great support, and very functional. I use them on my daily IS300 and the ride is excellent; others use them here for track and are satisfied.
As for your wheels - they are a fairly common size range and should fit fine without further work, with the caveat that you don't go too low. If you are too low your alignment will start getting out of whack and you will need more SPL parts to correct them. I don't think the fender clearance will necessarily be the issue, it's mostly sorting out side-to-side to make sure it's even and to zero out your toe for tire wear.
You'r eon the right path, just dont get intimidated by options presented.