I haven't done the AGX's, but...

1) The boots are nice to have, but not essential. I know Energy Suspension sells them, but you could probably get them from anywhere. Some people just don't like the shiny chrome to be visible, and it does help keep dust and wear down.

2) Can't think of any parts that you'll need to reuse or replace. Anything new comes with the new shocks. Everything else can just go back on. If you see something that looks worn...replace it later. (:

3) It'll throw your alignment off, but a shop should be able to bring it back on track.

4) The swap is easy to do yourself (provided the old ones come off easy), but someone's help is nice for putting the new ones back on.