Okay so i'ved removed the interior and there's several places that need to be cut out. I'm considering just renting a plasma cutter for a day. $38.00.
I've never used one how difficult and what kind of trouble can I get myself into?

 

You will still want to have a grinder, but a plasma cutter will make short work of the metal.

 

Ok cool..no pun intended.
You're gonna be hearing a lot from me in the near future.
I tried the lazy way and had a body shop quote the rust repair work....all i can say is holy crap batman. Guess i'm gonna learn how to mig weld. By the way is there any reason one cannot paint over a flux cored weld?

 

In the end, there will be no difference in the weld. You will remove the slag layer off of the top of the weld then finish the weld with a grinder/sander keeping the heat down. You want the weld to stand just a bit proud of the surface of the metal so that you can finish it flat with the surface for minimal body work after the repair.