your best bet is to get a magnet and run it over the car and find out exactly where there is bog and rust
what exactly is bare metal? is it a part and part of the shell itself? if its a part (door or whatever) then theres no issue and if its all god then prime it and proof coat it
if its a shell section your better off getting the rest done... where are you located? iv got a guy in syd that is going to sand blast the whole car except engine bay for $900... so thats the 2 doors, 2 guards, bonnet, boot, compelte shell outside and the door jams... so the engine bay and the inside of car and inside of boot not done
broken down this is $400 for the shell and $500 for the parts... what i ended up doing is paint stripping the parts and save myself $500 and am going to get the shell done properly... parts can be changed many times but the shell is the most important part and should be done right first go
there is no point painting it now when in 2-3yrs your gonna have rust spots all over... also with sand blasting they only do the outside of the bonnet and boot as it will rip the glue if done from inside, but if you get it bead blasted instead then they can do it inside and out with a smoother finish than sand... not many people do bead blasting but if you find someone then it cost the same
sand blasting is obviously grains of sand and bead blasting is glass
so to summarise i would sand/bead blast the shell and the rest you can work something out like i did... the issue lies with the fact that repairs have been done already... me every thing goes back to bare metal i dont care on costs
with your current situation all you need to do is prime whats etched and bogged only... you dont need to prime where there is paint cause paint sticks on paint... now if for example the car is currently BLACK and your gonna do it YELLOW then you need to base coat it first which basically is a silver coat first on top of the black and then the yellow as the yellow wont cover over black unless you spray 5-6 coats and thats just F!@KED doing that