on what to upgrade, but if you have a large stereo system, I don't think the UD pulley is a good idea. The NA alternator is rated at 80A and a 400W stereo system would be an extra 33A load (at full volume). With the UD pulley, you might kill the engine if you have it cranked up while idling.
If I were you, I'd invest the money. If you invest in the right stock, you might be able to turn it into a TT...