From my experience, it varies a lot from detachment to detachment and even from year to year. We had a couple freshman classes with T-shirt’s and jeans, some with polos and khakis, some with both and some that wore PT uniforms. Anyhow, I’d wait till the summer and call your det and ask. They should be in contact with you and give you specific information with regards to reporting, AFROTC orientation (my det did an orientation a couple days before classes started) and whatever else you’ll need. At this point, I’d just confirm with the det that you’re enrolled for the fall and that they’re expecting you.
For boots, definitely don’t buy them yet. You won’t need them initially (likely not till your sophomore year) and your det will get you some standard issue ones when you get a uniform. At that point, you can see what other cadets have and explore your options within AF regs. Personally, I stuck with the issued ones until after I commissioned and then bought some lightweight ones.