I have never seen a -6 offset wheel, but it depends on the brand name, but I think you will be happy with +1 and 12.5" tire, and if not you can try a spacer later on, cheers.
Just note that my tires are 12" wide, so if you use 12.5" wide tires it will stick out a little bit more, also my guess is with -12 offset and 12.5" wide tire you will need to do some trimming on the well liner.
Hello, new to the forum, here is my set up:
18x9 Fuel Maverick +1 offset.
Goodyear Duratrac 295/65.
Rough Country 2.5" leveling kit with 1" rear block.
No rubbing at all, love it.