OP: You need 3x sets khakis. Get a size larger than normal and tailor them down to allow for future tailoring after 'shrinkage'. Wear two, keep one inspection-ready set pressed/starched and rigged just in case. Don't be the guy up late frantically trying to make your daily-wear set look shit hot for a meeting with the skipper/PRB/Commodore the next morning and your future in Naval Aviation is hanging on it. Protip: it doesn't work, and when the Skipper or PRB's first thought when you walk in is, "What a shitbag," things will not improve from there.
Buy brown shoes. No one will ever be impressed by a SNA/SNFO wearing black shoes. It doesn't say 'I'm afraid of jinxing myself,' it says, 'I have so little confidence in my potential to make it through the TRACOM that I'm afraid to drop $40 on a pair of shoes'. The Bates Lights they sell at the NEX are fine.
Other than that, one set whites and one set of SDBs (with Ensign stripe, as mentioned above). Seasonal uniform change in the Gulf Coast region is usually April Fool's and Halloween. Odds are, you'll be there during a seasonal uniform change, so may as well take care of it. When one of your fellow ensigns dicks the dog, a sudden SDB/whites inspection for you and all your friends can and has happened.
Whether you need NWUs depends on the VT you go to and what their watch policies are, so you probably won't need them, in the uniform-of-the-day-sense, before you finish API. But I would submit that while in A-Pool/IFS/API, there will be days when you're otherwise untasked and need to go to Medical, PSD, STUCON, what have you. You need to be in uniform for that (NB: Ensigns taking care of official business in their beach togs will likewise impress no one), and if it's a choice between rigging and putting on khakis or throwing on NWUs, I'd go with the aquaflauge.