Check this out from Dan Checkoways' awesome site:
http://www.rvproject.com/rivets.html
This should answer your first question.
You'll really want both a squeezer and a rivet gun. I have a 3x that I like and a tungsten bucking bar (plus others), a pneumatic squeezer with 3 yokes (a 3", a longeron, and a 4" no-hole), plus a manual squeezer (a "Main-Squeeze" from Cleaveland Tools). I try to squeeze as many rivets as I can, but there are simply many times when bucking is the only way so it's a skill you have to learn--it's not hard, just takes some practice.
The dimple dies (male and female) create a depression for the manufactured head of a flush rivet (ie. an AN426) to sit in after it's set so the the rivet head is flush with the surrounding material. Typically you'll dimple metal up to .040. Anything thicker you'll machine countersink to form the depression.
I'm about to rivet my tailcone. You're more than welcomce to come over and check it out. I live just North of Qantico Marine Corps Base off of I-95, about 30 miles South of downtown Washington.
Hope this helps!