A decent metalworker would be able to cut out and weld in new metal over it. If it's spot rust, that can be ground off or a certain type of acid can be applied to get rid of it.. Bondo over rust is a horrible, horrible combination when the next guy comes along, 'cus usually it looks like crap and falls apart. Find a decent bodyworker, one that's been at the game for a while (old guys are always best, IMO), or a friend with a MIG welder.
You know the old addage...If you have to ask you wouldnt understand thing... Your going to need to be able to cut, fabricate metal, and weld. Hoods and fenders can be replaced, and they make alot of other panels. Either get some intructional DVD's or just admit to yourself your going to need to pay somebody to do it. A finished car is cheap compared to the experience and tools it took to complete.
Without actually seeing it, there's no way to tell. Try to preserve the original parts as much as possible since this adds to the value. But at some point it becomes not worth it and new parts become more cost effective !