You have done a marvelous job of describing the car. It may seem like a job that can't be done, but I have heard of worse case scenarios. The mechanical part of the car is relatively cheap to bring back to originality as compared to the body. It sounds as if you are going to have to replace all of the panels such as fenders, quarter panels, doors, floors, hood, trunk lid, etc.
Now, if you have a place to work on it such as a garage or barn where you can leave the parts out and get to them when you can, then you are way ahead. If you have welding skills, that's great, but if not, then you can take welding courses. You will need a good set of wrenches of all types, and of course a welder, cutting torch and air compressor with all the tools to go with it to include a paint gun.
If you are starting from scratch tool-wise, and if you don't have a place to work on it, you may want to wait until you get those things.
Also, if it is a plain jane coupe, you probably will have way more into the car when you are finished than it will ever be worth, but if it is a convertible or fastback, you may come out about even. I would say that when all is done, to include a new body, overhauled V8 engine, rebuilt transmission and rear end....and of course a new interior to include new glass and rubber all around......you are looking at around $15-17 thousand dollars, if you do all the work yourself. The problem, as you have already stated, is that we don't know the actual condition of the car, and we don't know your skills. If you have no skills, and aren't willing to learn and have everything done by somebody else, forget it. You will wind up with a $40 thousand dollar car worth 15.