pre-hung interior doors

I am about to hang 3 pre hung interior doors. I want to stain these doors before I hang them. My question is which way is best to hang these, with the door on or should I take the door off, stain them or hang the jam without the door and then put the door on after I insert the jam? My second question is I will need to cut the jam's width. These jams come in width's of 4 9/16 inches. One of my jams is 3 inches and another is 3 and 1/2. Is a circular saw the best way to cut these? Thanks for your help