I was sort of in the same boat as you. I bought my car off ebay during my last deployment. I am the third owner and the last one left it in a barn for 18 years after painting it red in a highschool auto craft class.
I had the usual rust areas, rear bumper mount, rear driver quarter panel, floor pans (real bad), fire wall, battery tray.
I found a body shop that will do the work, its going into the shop in about 3 weeks while on mid tour. The shop is going to run me just over 6k for media blasting, body work and paint. And its better to get it done all at once, at least thats my opinion. Getting it done in stages just drags out the agony of getting it done and driving it, again my opinion.
01ragtop is dead on, being a 73 you will have to do your homework for some parts and maybe even pay through the nose for others, just depends on what you want in the end.
I would suggest seriously checking into a few body shops, it doesnt hurt to drive to get to someone you feel comfortable with. You can always trailer the car too. Mine will take 6 months from start to finish, I am in no hurry though cause I wont be home again till Feb 09.
For the engine, are you set on what you got? what about a widsor or a stroked windsor or 302. Just some thoughts.