Yea, assuming nothing is wrong with it, that's a great deal, and you will love the sound of the Prochamber. What kind of mufflers do you have?
I re-used the stock manifold studs and nuts, but I put new bolts where the mid-pipe bolts up to the cat-back. And yes, get the passenger side flange gasket. I got one, but didn't put it on when I installed the pipe. Well, that was a mistake. Just go ahead and replace it. I think mine was $11 from Advanced.