First Triathlon, What to wear?

If allowed- you could go 'topless'. 

if it's a wetsuit legal race and you've got a wetsuit- than any sleeveless compression top might work just fine.

Or- Pick up a basic tri top for cheap at places like Sierra Trading Post (sign up for their deal-flier for extra discounts).  They swim well.

also- get yourself a race belt.  An extra $6-$10 investment.  It's a strap that carries your race number for the run leg, that you just clip on at T2.

Depends on water temp/if its a wetsuit legal race.

If the waters warm enough I would go topless for the swim and pull on a compression t-shirt for the bike/run.  I did this for my last 2 (and my only 2 so far!) triathlons.  The only problem I had was the first time my arms were too tired in T1 to pull the shirt over my shoulder blades!  Luckily there was a kind volumteer in T1 who pulled it down for me.  That said I would do the same again.

Good luck with your first triathlon!

As already suggested, you can either go topless or opt for a tri-top, since you already have the shorts.  If you opt for a tri-top, it should fit tight, and you should plan on wearing it for the swim--you'll lose WAY too much time in T1 trying to wrestle on a tri-top when you're wet.  For shorter races I prefer a tri-suit (or if it's really hot out, just tri shorts), but it's just personal preference.

You're kidding, right?  I had the exact same shirt (it was a pretty snug fit), and it took me at least 30 seconds to get on in T1.  I recently bought a sugoi turbo tank, which is great, and my last T1 was 0:33.