Auto body repair & detailing: body panel replacement and paint, arc welder, spot welds

Question
Ok I have a 1992 Isuzu rodeo, and in the back, on the jam between the roof and the hatch, it is rusted through. In addition, the roof itself is rusted through in a few places. Now my local body shop wants $3,500 to fix! of course I can't afford that. Besides, I am more of a do-it-yourselfer, anyway. From what i can see, it looks like all i need is to drill out the spot welds, and replace the assembly as a whole, since it cant be repaired. Now what I need to know is, how do i go about putting the replacement panel back on? I think (correct me if I'm wrong) that a spot welder is just an attachment that goes to an arc welder that looks like a gun with 4 prongs. How do I use it to weld the spots together? And I am going to repaint the whole body myself. how should i prep the body for a full repaint.. Can I sandblast? What type of primer should i use? I want to use enamel paint.

Answer
My advice,drive it in the ground.You are on the right track on drilling out welds but the arc welder is a bad idea.Mig welding is the preferred method of panel replacement and sand blasting is a big no no.You can sand blast small areas or areas where the metal is thicker.Sandblasting will generate heat and warp the panel and create bigger problems.You will need to use a D/A sander to prep the body for paint.Depending on your choice of material 320 grit is the norm for refinishing.