I just ordered a new 2016 Rancher DCT IRS EPS and want to get a head start on accessorizing. First question is what are my wheel and tire size options?

I previously had a 2008 Rancher (SRA) that was stolen and I had 12" ITP SS212 wheels with 27×9.00-12 Maxxis Zilla fronts & 27×11.00-12 rears.

I plan on sticking with the Zilla’s but am not sure what tire sizes I can get away with. With the rear IRS, do I need to worry about the offset? Also, what is a good place to order from?