First of all we need to know the shape your Vehicle is in before some one can give advice .
Is it rusty ? Is it pre primed ?
If its primed I would recommend having it blasted with Aluminum Oxide and see what is under it all , some scary stuff can be hidden with Fiber glass , Bondo and other fast fixes . If its clean and in fairly decent shape after having it Aluminum Oxide blasted , prime it with PPG's DPLF Primer Sealer and then you can do your repairs with filler . The few replies here have very good info and you can go with that .
But I wouldnt do anything till I knew what shape the body was in . it could come back and haunt you after spending much time and money not knowing what shape its in .

They have what is called Cheese Graters for shaping bondo .
There is a right time to use the Cheese Grater for shaping to soft & it will just rip it off the panel , to hard and it will not work . This will take some getting used to to find the right sweet spot for shaping

Hope this helps