This is Steel wheels only
15x7 was standard, 15x8 was optional, both has 4" backspacing.
You can put anything larger than 31x10.50 on a 4x2 and expect it not to rub, they will physically fit on a 15x7, but they are better suited to a 15x8.
largest tire is a loaded question. are you talking width or height. Height is going to be limited by lift, width shouldn't be over 10" in my opinion.
Again, loaded question, width or height...I ran 33x12.50's on 8" rims which I consider the widest, but wider is possible and rockcrawlers put wider on there because of the inner bead
Width of the wheel is determined by the area INSIDE the lip. Factory wheels are stamped with their size and width though.