I bought a fixer uper, though slightly newer (92 325i) and all I can say is if you can do a bunch of work personally your smart, if you need a mechanic to do most of the work your stupid (aka me)
As for the pot smell, i have a little more uh... expertise. It should go away in a matter of a few weeks MAX depending on how much partying went on in the "palace". But you can buy air fresheners (OZIUM is my favorite - just don't go in the room/car you sprayed it in for 15 mins) that can kill that smell in a day.
But vacuum everything and check the glove compartment and any areas where small peices could have accumulated. Depending on the cop and how good of a day he is having, you could get busted for a single miniscule shred of pot (depending on the state you are in).
Hope that helps