Fuel Mavericks: considering changing offset...

2021 Crewmax 4x4:

Hello, I currently have 20"x9" D537 Fuel Mavericks with a +1 offset & 285/55/20 KO2's. Looking at going to the exact same wheel but bringing them in a little with a +20 offset (if I'm doing my math correctly).

Also have a 1.75"-0" RC leveling kit. I just don't like how far these wheels stick out and sling stuff everywhere and also would prefer the look if they were in a bit. Bought the truck with 1,200 miles and thought these would grow on me but I've decided that I need to bring them in a bit. I also installed 3/4 flares which have helped a bit.

Questions:
1) If I do this, will I need to install a bumper shim to help tire clearance? (1/2"?)
2) Wheels have 8,000 miles on them and are in MINT condition, what are they worth?
3) Best site for buying wheels only?

Thank you in advance.