very easy to answer: stay away from rust. If there is any at all, you are looking at a painfull experience. Start poking into rust bubbles and the e9 starts unraveling. It really is the biggest downfall of it.
Interior and mechanicals are a lot easier to fix or live with. Plenty of parts easiliy obtainable. Only really worn engines are getting harder to replace cheaply, the days of an abundance of good used engines are gone. Still, reabuilds are possible to a very high standard, only the parts and labour costs do stack up.
So: avoid a rusty car and you´ll be fine.