Oh, for the tires. If you can find a way, go with a 17" rim, with a 5 x 5.5" bolt pattern. Few reasons:
The bolt pattern is the most common for aftermarket and will swap over to 3/4 and 1 ton axles in the future. If you run 37's, those axles are in your future. Save 4 grand and only do the tires and rims once.
A 17" rim is big enough to fit on any brakes all the way up to one ton stuff, but is still very common for tires, making them affordable. The 17 is the new 15. You can get comp tires in 17", used tires are more common, and almost every brand does every tire in that size. 20's are more money, and harder to source.
Lastly, 17" aftermarket rims are cheaper and easier to source then 20's. Specially the beadlocks. Used or new, 17" beadlocks are everywhere. 20's, not so much.
hth