Need details on '03 2.7T Hi-perf Wheel/Tire combo
The stock 17" I believe is BBS which are of very nice quality and are usually very light(a + in ride and handling as well as acceleration and fuel economy). You should keep the stock tires with wheels and just buy a set with tires(why have stock wheels sitting around without types; you could used them for winter or for taking long trips where 18 or 19 inches rims will more easily damanged. Most shops will charge over $125+ just to swap tires for you so why bother unless you plan to sell your stock wheels.
Go to 18 or 19 will greatly enhance the look of your car but you have to watch for the weight gain in most cases unless you spend lots of money.
There are plenty of different sizes of wheels you can go with from 7.5, 8.0 to 8.5 for 18" to 8.0 or 8.5 or even 9.0 for the 19". I would go with 18x8.0 OR 19x8.5. please try to stay light as increase rotational mass can greatly reduce performance.
Don't see the point going with aftermarket 17 unless you wanna to different and with limited budget, stocks looks just fine with me and hard to find good looking 17 compared to 18 and 19



