Original belts? Wow, that's amazing. If one of those belts slip or break, you are looking at a 2500 dollar repair bill. It's expensive but the interval for belts should be around every two or maybe three years or 30,000 miles. Right now, you are on borrowed time. This is one of the most important parts of owning these cars so try and learn to do it yourself so you can afford to own this car. Are you mechanically inclined or do you have friends that work on cars often? If so, you have a better chance of keeping this car going. The belt job is usually around $1000 to hire it done and about 275 to do it yourself if you change the waterpump at the same time. If not, about $175. They are expensive cars and for a college budget, it's going to be a tough road for you...in my college days, there would be no way I could afford one of these. There are a couple of web sites that will bring you a wealth of knowledge and you should read them and visit them often. Another thing that is fairly inexpensive to do is the oil cooler seals...do them before they go. They are more likely to go on an 87 than any other year...one of the web sites will warn you of that also. Of course I learned the hard way and I'm now replacing an engine. It's about 50 dollars in parts and alignment tool and a fairly easy job to do. If you choose to do it, PM me and I can loan you my alignment tool and save you 20 dollars.
You are correct about these being fun cars and handle like a dream not to mention that they look really cool. Clean up that mold and stuff and spray it really well with something so it's not a health hazard. That probably indicates the sunroof is leaking meaning the drains are probably plugged. Do a search on sunroof drains and there will be posts on how to clean them.
Well. here are some web sites for light reading...
www.clarks-garage.com
http://www.connactivity.com/~kgross/FAQ/944faq05.html
www.924.org
There are many more and you'll learn what they are but that's a start. Welcome to Porsche ownership and welcome to the forum. Come back often and good luck with your new car.