Wow, I'm surprised nobody saw this before me since I'm hardly ever on here.
Re: Prior Flight training... It might help. Having a PPL will allow you to "skip" IFS, since you theoretically already know how to fly a light civil aircraft, so you can get in the pipeline a little quicker. Instrument flying experience can help you break out in Primary, as it counts for about 50% of your overall average (or it did 6 years ago, I don't know how much that's changed.) That said, I have known the occasional guy with 1000s of hours who had trouble going "back" to being a student in the cockpit. Stay humble and be eager to learn the Navy way of doing business, and you should be OK.
I went in with a private license and about 100 hours and did fine. If it's platform selection you're worried about, that can have as much to do with timing as it does with your ability. Don't get discouraged by that though, most guys like what they end up flying.