The two best books for general information about 'stealth' technology and applications are:
- 'Lockheed Stealth' by Bill Sweetman
- 'Skunk Works: A Personal Memoir of My Years of Lockheed' by Ben Rich
But if you want to know more about 'low radar observability', which is the more correct phrasing used by radar community, then you have to spend a lot more money on formal texts and dissertations by professionals in the field. Hundred$ or even thousand$ depends on how in-depth do you want to go. Mine was approaching the thousand dollars mark when I finally received IEEE access thru a previous employer who does contract work for the USAF and USN in the radar field.
As for joining the USAF, what do you want to do? What do you have to offer? How long will it take to go from freedom to Basic Training in TX? As soon as you and the USAF can work out a deal -- next week or next month. Depends on the training cycles. Talk to the local recruiter. Cost you nothing but time.