If you are going after a rated slot (pilot, nav, ABM, etc) from ROTC, then getting a direct-ascension AFIT slot will be very difficult (read: near impossible). When I applied for it, they actually quoted that not only was I ineligible due to being a 92T0, but since I was a December grad, I was even more ineligible - if that makes sense. I pleaded my case up several levels to no avail, including to the 3-star AU/CC when I was at Maxwell for ASBC. From what I can gather, if you want an AFIT slot and fly, either go the 62-route and try to apply for the rated board, or get your wings then apply to AFIT. I definitely recommend the first option over the second after talking with some friends who are at AFIT currently and some who already graduated. For me, I just stuffed the AFIT idea and got to work on my masters (a M.Eng. actually) while I waited for UPT to start.
As far as post-AFIT, the only stipulation is that you have to work in an Advanced Degree (AD) coded position upon graduation. However, if you are going to UPT or UNT, that requirement is waived. You keep your assigned AFSC throughout AFIT, and just go on to your job after graduation. If you still are interested, make sure you completely read all of the associated AFROTCI's, Holm Center I's, AETCI's, and AFI's having to do with AFIT Direct Ascensions. When you make your case, it always helps to have ammo.