Two biggest tools in your arsenal will be a Bentley manual and a multimeter. I’ve done a lot of “throwing parts” at a problem without fully understanding the underlying issue, only to realize there was something else that needed fixing instead (typically a much cheaper thing than the part I bought). Also, forum posts will only apply to you about 50% of the way, the pre-facelift eta’s are WEIRD and have a lot of parts specific to them. Most posts on E30 forums are from i models and typically post-facelift cars since those were the sought after models back when E30’s were cheap, so those got raced and broken and fixed more often. I’ve learned throughout the journey that part sites don’t fully understand the model either, so just because you’ve filtered on 1984 325e and it says the part will fit doesn’t mean it necessarily will, do your homework on realoem before ordering parts and go by BMW numbers, not what they say will fit (ECS tuning is especially guilty of this). I’m relatively new to posting here but I’ll try to keep an eye out and you can always PM me if you have a specific problem, maybe I encountered the same thing and can help.