I would suggest you to ask on official Nobara discord. I got help right away.

Windows.

For spider man recommended gpu is RX 580. I would suggest you, of course if you can afford, to go for RX 7700 xt or 7800 xt. You will be more future proof.

That all depends on what games you play. Do you want to play new AAA games or retro? Indie? What is your budget? XT is stronger version of regular 6600.

I don’t think there will be any issues. On that note, use open source AMD drivers. You dont need proprietary one from their site.

AMD all the way. Few weeks ago I finally made a switch from Nvida for the first time. I have no problems in gaming. All games that I play run same as on windows.