I wouldn't get a low or negative offset wheel if you aren't leveling or willing to do some trimming. I have a 3.5" lift and I still rub on both the front and rear of the front wheel wells. I'd venture to say my -18 offset with my 10" wide wheel has a greater impact on the trimming and rubbing than the tire size does. The tires are only roughly .9" wider in diameter than stock, which is only less than a half inch wider from the center of the wheel (figure how much closer the tire is to the things it could rub on). The offset is what creates the need for the trimming more than the tire, when turning the wheels and moving up and down with the suspension.
The offset matters because when you turn your wheels, your wheels/tires stick out further than before, effectively creating a larger radius from the mounting point, which is why you have to trim to accommodate them. There's some good graphics out there demonstrating this, so you can better understand. But hopefully this helps clarify some of your concerns.