Just did my front seal. It's super easy to do. the hardest part is getting the old seal out. I got mine out with a cheapo harbor freight seal puller, a screwdriver and a hammer. You just have to work it for a little bit for it to pop out.
As far as an impact, it sure makes it a lot easier to just zip it off, but it can be done without it. I had trouble torquing the nut because my torque wrench was a tad long and hitting the ground but i eventually got it to spec. Make sure you get a new pinion nut too!