Thats one of those "pick your poison" deals.
If money is the issue, thats a deciding factor IF you want to be cruising this summer......you probably have tons left to do on thecar and money will be needed elsewhere for sure.
Media blasting the old fenders will cost you something unless you have the blasting equipment....and repairing them will take patience....which I have none...LOL.....
I it were me, and getting her running by the summer was key, I would get her mechanically sound....drivetrain, etc....fenders are easy enough to replace later. If the fiberglass fenders can be tweaked enough and easily enough to fit headlights, and look ok, use those for now and work on the originals on the side after the rest of the car is together.
I would prime and seal maybe and not paint...that way you can drive her around until you can swing the fender work or replacement and then paint the whole car at once.
Of course, doing it this way means extra work later....repriming if needed.
Dunno.....thats a tough scenario.....may just be better to somehow find the cash now to have the fenders blasted and patched and you do the finish work? How good at metalwork are you and do you want to learn on this car or prefer to save thetime and let someone else do that?