I'm a former AFROTC cadet and I took the AFOQT. I didn't study much for it and I don't have a very strong math or engineering background, and I did pretty decent (average scores, not all that competitive). Many of my friends who stayed in the program and commissioned with pilot slots did very well and from what I recall, nearly none of them had engineering degrees. In fact, one of them scored around 98 or so for Pilot and Nav and he majored in Business.
Pick something you're genuinely interested in and that you would enjoy doing if you don't get the Air Force gig, and pick something that you realistically think you'll do very good at because GPA is a big factor in getting a pilot slot in the Air Force, if I recall correctly. If you truly want to do Aerospace Engineering and you think you'll be good at it, then go for it, but don't pick it just because you think it'll give you a leg up on the AFOQT. It won't necessarily do any more for you than studying the right things will, regardless of what you major in. If you don't like it or it ends up being more than you bargained for, it could backfire.
Flight hours are factored into the PCSM score (Pilot Candidate Selection Method) and indeed can improve your chances of getting a pilot slot, but for AFOQT purposes, most of the general aviation questions were fairly basic and I've been told they aren't any more difficult than anything you'd encounter on the Private Pilot FAA Examination. Plus, if I'm remembering correctly, the calculations for how flight hours affect your PCSM are tiered, and the more hours you accumulate, the less impact they have on your score, so there are diminishing returns. Getting your PPL would certainly be a good thing and I encourage you to do so if it's within your means, but going significantly beyond that may not be a huge advantage if you're doing it solely to try to do better on the AFOQT and get picked up by the Air Force. Get your Commercial rating if you really want to and it's not going to jeopardize you financially, but it's not going to make or break your pilot slot chances, so don't bet on it.