Congratulations!

I don't know (nor is it important at this point) what you paid. You have bought a fine car. At the low mileage you stated, I wouldn't worry about timing chain maintenance unless the preventive maintenance, particularly oil changes, has been neglected. Rubber items such as window and top seals should be o.k. unless the car has been outside it's whole life. Low mileage also means that the engine compartment hasn't had too much of a heat soak thus deteriorating rubber engine and vacuum components.

The center vent issue is something almost all of us deal with. In my case, I hold the center vents open with a 7/16 wooden dowel inserted through one of the vents from the front. I will get around to fixing it the right way some day but it is not very high on the priority list. The a/c will cool nicely through the side vents anyway.

These cars are very robust and you have bought well. I have an 88 560SL bought long distance on EBAY and found that the car had much less wrong with it than the seller thought. They are easy to troubleshoot if you are so inclined using a repair CD and/or ALLDATADIY. If you are not willing to do your own repair and maintenance, be prepared for some sizeable labor bills. Parts are readily available from many sources since they are a long-lived classic. Sort of like an old Harley Davidson.

Enjoy the Ride!