You need to get a look at the body first to see how bad it is. They are unibody cars and if stored badly, there may be too little left to save the body...ie you would end up replacing everything with new or donor body parts...and if that's the case you are better off swapping the VIN onto a donor. I tore apart one with JDM1602 a few months ago that had been sitting for 15 years and the body was falling apart in our hands.
PM me once you see it, glad to offer some suggestions once you know what you're dealing with.
70 2002 M2 2.5L build
94 Euro M3 race car