honestly i would build the 2.slo before i would do anything else to the car(it is cheaper)... you mentioned track in your post what kind of track do you plan on running at drag/road? b/c those are two completely different setups.

personally i would pick up a used SC; they don't make much power but very reliable and perfect setup for mnt runs or road racing.

there are a few turbo kits for the 2.slo but if your going to go through all of that i would just either upgrade to a nicer car not golf or do a vr6 swap + boost. 1.8t doesn't make enough power to go through all of that trouble. i've seen s4 go for 9k; i'd buy one of those and put GIAC on it and call it a day.