If it was me, (which im going to be doing the same soon)

I'd just use all 6k to get a newer nicer car. (no payments)

I know you dont wanna have a fully stock car, but just spend 5k on a nicer car then 1k in a decent stereo and tint, and tune up.

But if your gonna get the teg.... Get a alarm, its still going to be stolen for no reason...