84 733i electronics fun

Hello, a newbie here. I recently picked up an 84 733i in beautiful condition, except for the desert sandblasted paint, and the fun I expect to have with the body electronics. any thoughts or experience would be appreciated. I'll start out by telling you I am an ase mechanic, formerly with my own shop. I have mitchell, but it doesn't go into enough detail with diagnostics of the chassis systems. So I have a 2 owner car, wih the latest one being a dyier with limited skills. Me thinks he may have tried a few things. I have a tach/efficiency gauge that does not work, a gas gauge that doesnt work but the low light does and I have already tested the sender (itS ok) no cruise, no central locking system and as it gets colder, it's starting rough and needing to warm for a few seconds before it will run right. It's also a manual four speed with OD.