How wide can I go on wheels and tires without rubbing?

It depends on your chassis, offset, ride height, and how much fender work you'll do. The safe path is to copy a documented fitment for your exact car at your target ride height, then dial the last few millimeters with spacers rather than living on the edge of a rub. Lowered cars rub sooner at full lock and over bumps; a fender roll, mild camber, or a slightly narrower tire buys clearance. When unsure, size down.