new member tire/wheels questions- max tire size and bs needed to make it work

I am looking at running a 20 " wheel as a backup option with 35,12.50 -20's but still need to know the proper backspacing
 
I would like to run some 22's with the kuhmo road venture mt kl7 i believe in the size 37x13.50-22 but i need to know the proper bs on the wheels i was looking at some ventivs58 or some asanti 145 but they are kinda high. I woould prefer to stay away from the total chrome wheels so help please, and btw anyone use the h2 fender flares did u get them from hummer or aftermarket and i am having a hard time finding  a hummer aftermaket reseller i have had jeeps and they are easy to find anthhing for i thought the hummer would be easy to fond mod choices as well
thanks
Brandon