Looks like a fun project! Took me over a year to find an acceptable E36, had a bit of a rough interior but was very well maintained mechanically. There's a fellow on bimmerforums that put together a nice series of videos going over some good points when inspecting an E36 M3. I personally found them pretty helpful:
https://www.youtube.com/playlist?lis...R2sNb6Z6TGOAkq