Here's some thoughts with regard to your questions concerning synthetic oil, a K&N, bra and tires. First, I'm planning to run Amsoil synthetic in my car. In fact, I've purchased the oil, I just need to find time to put it in the car. Second, I'm using a K&N that was meant for a 2002. It fits perfectly in the 2004's air box. Concerning tires, my car came with B.F. Goodrich tires. I believe that they are 225x55x17 and are "V" rated. Finally, I haven't seen any bras for these things yet. I am also looking. Hope that helps. Good luck.
_________________________
2004 Polo Green WS6 GTP