"Do I need to get/would it help to have a PPL?" is asked so often around here, I think it's a prime candidate for the Banned Questions List. (Answer, BTW, is no, though a few fam rides/lessons aren't a bad idea if you have the time and money)
You're not going to the Academy to be a pilot. You're going to be a Navy or Marine officer. There's a lot can happen between I-Day and graduation. Even if you're totally PQ'ed for pilot, it may not happen. There were about half as many Navy Air billets for the firsties my plebe year as there were by the time I graduated; it was Clinton-era DoD budgets, and if you read the papers, the Government isn't exactly flush with cash nowadays, either. If you're okay with the idea of working your ass off for four years and then winding up going SWO or whatever because other options are closed to you, then go for it.
Here's the thing, though: it really is worth it, even if you destroy your knees playing fieldball firstie year and don't get commissioned at all. It's a good education, free, and looks great on a resume. Not many schools can say that.
Anyway, you're still a freshman, so for the time being concentrate on not farking up too much. About the middle of your junior year is when you need to start the machinery for admissions. In the meantime, take advanced classes and do well in them - they'd rather see a B student in AP/Honors than a A+ student in basketweaving. Play a sport and stick with it - they want to see a candidate with some physical ability, rather than a total bookworm/schlub. Do something that demonstrates organization and leadership ability. Admissions knows what a 'joiner' looks like, and belonging to 30 different clubs and not doing anything particularly much with them doesn't impress anybody; much better to do a couple of things, stick with them and grow into a leadership role. Summer Seminar has been mentioned, and it's a good idea. Lets you see the school, and lets the school see you. If they're still doing the 'spend the night with the Brigade' deal, do that too. The Yard looks a lot different in the middle of February. Keep in shape. Don't get in any big legal trouble, avoid experimentation with anything illegal, and don't get some girl knocked up.