Drifstix,
first ask yourself how serious are you about this car and how far do you want to go with it. Is this car your daily driver? If not then bodywork. This is the area that will potentially cost you the most just to keep it looking like a sprinter. Pull the thing apart and take care of the rust properly. Pull off the interior trim around the rear 3/4 windows and check for rust. Do this on the outside as well. Pull off the rubbers around the doors and boot, these things can hide alot. Cover all the usual spots. Then strip the car and get the body ready for a respray. Do as much as you can as this will save you heaps and you will learn alot too.
I also bought my sprinter with the engine work done but the body was fucked! It took alot of effort to fix it and would have cost thousands if i didn't know the right people.
Good luck with it.