First off a thorough inspection of all mounting location for cab doors hood fenders and bed. Check floor pans cowl inner fenders. Find out how much work it really needs or any portion of the truck that need major attention. Do'nt want to get to far into it and have to redo something you've already done. You can pull of all the trim and strip/paint. make sure window roll up good and latches work. Start making a list of thing that need replaced. Between the gentalmen (and ladies) on here and Ebay you can find a lot of parts. LMC Truck, classic industries and numorous other places have parts. Shop around for the best deal. Never stick to one source.
What year truck is it?
Don't get frustrated. it's going to take alot of time. I've done many cars and trucks and patience is something you must have or you're wasting your time. Have to make it something you enjoy or you're better off buying something already complete.
Good Luck!!!