You would have to raise your car with a jack if you did it yourself, but you would need 2 Jackstands for each end (4 total). You need good support for the car considering you would be working under a ton+ of metal. Its only something you should really do if you have at least some experience with it.
It sounds to me like you should just get it done somewhere. You don't have to take it to a dealer, but just any local shop could put an aftermarket exhaust that you purchased elsewhere considering it would be a bolt on. It should only cost somewhere around a $150 bucks for general installation, but probably not more than that. Snap-On and Craftsman tools are the best I use. MAC tools are very good too. I suggest you invest in a manual to help you learn everything about your car.
I have an 8 year old stock exhaust myself and its somewhat loud. Its a little bit of a performance sound that I find exists in pretty much all BMWs. If it concerns you, have a mechanic check it out for you. He can put it up on a lift and do checks for any exhaust leaks. Again, it shouldn't be near as expensive as a dealer would charge. An exhaust leak would more or less sound like "blowing a raspberry with your tongue :P "
5 Speed Manual
Alpine CDA-7895 Head Unit
12" Alpine Type-R, sealed box
Pioneer 400w amp for $20 at a yard sale (to replace my fried MRV-1507)
Infinity Kappa 4" 2-way speakers(rear)
Infinity Kappa 5.25" component speakers(front)
Debaffled airbox, K&N filter
Tracked Mud on carpets
Shampooed and cleaned carpets