I recommend starting with a +3mm offset.

I've seen some folks here with upwards of +9mm offset with the wheels and tires tucked inside the body, but their camber is at nearly 10 or 12 degrees. Play with the camber to see what you can get away with. I've seen drift tires with shaved edges to increase clearance by a few millimeters, too. Also, mount your body just a little higher than you normally would and soften your shock absorbers a bit to get the car to break loose easier.