Hey guys and gals!

New guy here and I'm looking for a little advice. My current DD is an 88 Jeep Wagoneer XJ, but I want to get something a little more economical as a daily driver while I do a complete restoration to the Jeep.
A friend of mine who owns a car lot has a nice looking 89 Audi 100, inline 5 cyl. with 175K on the clicker and an automatic transmission. I haven't driven it yet since the alternator is being replaced, but from what I see, it looks really good.
There are no oil spots under the car, the interior is excellent (except for the headliner falling down), body is straight and all the glass is good. My questions are as follows:

1. What is the maximum I should spend if it runs out well?
2. What kind of gas mileage can I expect to get?
3. how hard/expensive is the general upkeep (bearing in mind that I do 90% of my own work on my cars)?
4. Are the early 100's known to be problematic? If so, what was wrong with them?

I'd like to hear some experiences from folks that have had these cars or worked on them as well. Please let me know what you think, positive or negative, about the Audi 100. You will help me make my decision, based on what you have to say.

Thanks very much for taking the time for me. I look forward to hearing from all of you!
Have a great week and DON'T work too hard. They don't pay you enough!