1. Dashboards crack because the PVC and foam/vinyl top layers dry out under UV light and then crack. The best way to protect it is to use a windscreen shield when it's sitting out. I recommend not using Armor All, since it uses dimethyl silicone oils. These penetrate the dash and, when you stop using it, will actually accelerate cracking. Check out Auto Glym's vinyl care available at Canadian Tire.
I would just replace it. You'll never get a proper OEM look from any repairs. Unless you can somehow get the stock vinyl and fill/rewrap it. (unlikely)
2. Usually your resistors have heated and cooled so many times that they are bent and touching each other. The 4th setting bypasses this and will work no matter what. Open the cover at the back of the engine bay on the firewall and the blower pack is on the bottom side of the blower. Junkyard or R3VLimited.com for a used but still good one.
3. You need to rebuild your lock. These locks are made with pot metal, or white metal, and are very brittle. Also, the type of bearing used in them is sub par. All sorts of parts will break after 25 years of usage. Look at PelicanParts.com for a lock rebuild kit, they're about $30. Very easy to rekey and rebuild your lock at home.
Here's a guide I used: http://www.billswebspace.com/BMWE30D...derRebuild.htm
4. Over the years, your selector rod and the various bushings will wear out. This will cause high amounts of slop and play in the shifter. Autopartsway.ca sells all the needed bushings. Check that your selector rod is straight while you're in there. I ignored this problem and ended up cracking my center console in my old car.