I've done a few pad/rotor changes on tegs and it is very straightforward. An impact should work on those screws but since I didn't have air tools the last time I did the change I used an impact screw driver that I purchased at the auto store for $15. It is a screw driver that you hit with a hammer to provide the inward pressure and torque to release the screws. There is probably a better chance of not stripping them out using this as opposed to an air gun, but you'll probably be fine. I've been using channel locks to push the pistons in. The grease I've been using comes in little packets from advanced auto for $1 and have not had any squeaks at all. The only thing I'd recommend doing is bleeding the old fluid out completely once you are done as brake fluid absorbs moisture over time.