I’d hold off and get the wheels as well as tires all at once, should go with a 0 offset. OEM 20s have a +18 or so offset so you may have a slight rub, if no rub the tires will look tucked.
I have Bilstein 5100s set at 2.8 with Zone UCAs running 275/65/20 and went with Supreme Suspension 1.5” spacers. This untucks the wheels/tires and gives me a -18 offset, which is a bit on the wide side for me but the stance is very much true off-road truck like, so I can live with it till I change out for 35x12.5/18 and 18x9 wheels with a 0 or -12 offset. Here’s a couple pics for reference:
Also, I’m running a Zone 1.5” body lift so I appear higher than your typical level and I really need some larger tires to fill out that wheel gap appropriately.