If you have no maintenance history, you have to assume that it has not been kept up, There could be a lot of things that need attention with a car this old. You may want to spread these things out over a number of weekends to ease the burden on your wallet and time.
1) Check all the plastic and rubber tubing between the air filter and the throttle body for cracks.
2) Check all the plastic and rubber parts in the cooling system for brittleness and cracks.
Look carefully for seepage from the top radiator hose connection, the radiator end tanks, and beneath the water pump and thermostat housing. Seepage is a warning of impending failure.
3) Check the outboard ball joints, the tie rod ends, and the suspension bushings for looseness.
4) Change the oil
5) Change the coolant (use BMW brand coolant)
6) Change the brake fluid
7) Change the transmission oil (automatic or manual - no, it is NOT really permanent)
Inspect the guibo in the drive shaft and the U-joints while you are under there.
8) Change the differential oil
High quality parts are available on line from a number of vendors. I generally use Autohaus AZ, but I could name a dozen excellent parts suppliers on line. There are so many good ones that the bad ones have disappeared. Just avoid Chinese-, and India-made parts (which now include some well-known name brands).
If the above has not thoroughly intimidated you. You might want to read the following thread:
http://forums.pelicanparts.com/101-projects-discussion-forum-bmw-3-series-e30-e36-1982-2000/599896-advice-buying-e36.html