Hi XJ and welcome to the forum. Mate, i started off taking my XJ to a mechanic, but frankly, you are better off sitting down with a cup of coffee and reading this
http://www.ebay.com.au/itm/JEEP-CHER...cAAMXQkN1RzpOb
Not only will you save yourself over a $100 an hour, but you will understand your Jeep.
The Full Service Manual is also downloadable on this site for free!! Have a read through this forum at the usual problems XJ's have, and with a few tools, there is nothing you cannot do.
http://www.ausjeepoffroad.com/FSM/XJ..._Pre97.pdf.zip
http://www.ausjeepoffroad.com/FSM/XJ...Post97.pdf.zip
If your jeep is running OK, and braking OK and driving OK, then, as you have just purchased it, i would look at an oil and filter change. Also, check your airfilter and brake pads. If your brakes feel weak, as mine always did, i would recommend EBC Yellowstuff. Expensive, but it was the only thing that made my brakes work and i even swapped out for a new booster at one stage.
If and when you need parts, don't panic at the prices. You can find stuff very cheap on Ebay and rockauto.com
Cheers,