Suppressor Help

Have been thinking about getting a suppressor but don't know anything about the subject. Not sure what would be the best caliber to buy for either. AR in 223, lever 45 colt, 9mm for the new Dagger? The one for 9mm would it work on say a .357?
As far as paperwork I'd like a trust so I could add my wife and grown kids to it. Haven't a clue on any of that either. If you do a one shot trust can you add people after and how hard is it? Or is there a easier way of doing it.

So any of you guys that are suppressor literate please school me up a little bit.