[Freon]

4/32nd with a performance tire in heavy rainful is going to start to be hair raising.

You can get a real treadwear gauge for a few bucks at the auto parts store. I have one that reads both in 32nds and mm. I don't care for the penny method.

You can't really rotate, but you can have your fronts dismounted and swapped/flipped, and rears dismounted and swapped/flipped. But that's a full mount and balance on the entire car. You can manage wear with tire pressure and proper alignment as well. Oprtimal alignment may depend on your driving habits. More aggressive drivers will probably want some extra camber in front.