If you earned the rank of E-3 before AF BMT, would you receive the pay of an E-1 or E-3 while at BMT?

You will get paid E-3 beginning on day 1. Whether or not you actually wear it depends. In the Air Force, probably. I went to basic training at Ft. Leonard Wood, MO. We were not allowed to wear rank at all during basic. Except on our class A's, because they were sewn on when issued. But we only wore them for 1 inspection and graduation. I was an E-2 due to ROTC. I was supposed to be an E-3 but my recruiter screwed up the paperwork. He used the standard recruiter line, "oh they'll fix that once you get there." Yeah right. But we had several E-3's and 4's who also did not wear rank, but got paid for it. But I had friends who went to basic elsewhere, also in the Army, who said they did get to wear it. So I guess it's up to the post commander. In AIT though those few of us who had rank had to wear it.

0014 is absolutely wrong. He obviously either was never in, or went in an E-1. You will receive E-3 pay starting day 1.

If you enlist as an E-3, you will wear the rank and receive the pay of an E-3 right from the start. If your E-3 is contingent on completing training, you will receive it once those conditions are met.

Once your out of boot camp you'll start getting normal pay. I hope you're not one of those snooty ROTC kids. No one cares what "rank" you had in high school.