I think you'll come to love your e23 as much as I love mine. It is a great car that with good maintenance will last over 300k miles. The HVAC is balky but with patience, DIY fixable. The instrument cluster has a lot of little problems, but for the most part is also DIY repairable.
Here is the overall checklist I like to give people:
http://bimmer.roadfly.org/e23/messag...w11/25654.html
It is for the e28 (5-series) but ports over well for the e23. Here is another link with a LOT of information:
http://www.e38.org/e23/
Also, and this is really important, become a member of the e23 forum on roadfly.org. There is so much information there from an excellent, friendly, group of e23 enthusiasts who will share their knowledge with you freely.