I am looking at getting new tires to put on my stock 16 x 7 rims. From what I have read, I have a little trimming to do on the mud guard, but does anybody know if 31 x 10.50s will fit in the well with the 16 x7 rims, or would I be better off with 30 x 9.50s?

No matter what (pretty much), you'll need to find a metric size.

A 265/70 16 is the stock size on an SE, and is about 30.6" in diameter. Going to anything smaller would be pointless.

Serach this forum a bit, and you'll find plenty of threads on tires and sizing.