first of all, don't obsess about making your scooter 100% dialed constantly. it really doesn't matter what it sounds like when you drop it, just ride the thing.
second, don't buy new bars. the ultra pro bars are fine.
third, don't get anything except grips and griptape. after you ride it for awhile, start working your way up and getting little things like brakes, cheap metal cores, and a headset if you'd like. (threaded headsets spin much faster, threadless headsets are smoother)
there's no point in buying an ultra pro if you're going to replace every part except the deck anyway. that's my advice. actually, i really like threaded/stock stuff because the headset spins fast and it's pretty light. the only problem is when you're more advanced trying bigger things, you're going to break your stock parts. once you see alot of wear and tear or breakage, then buy new parts.