D.D.
I don't know the answer to the second question. But to your first one: this is second-hand, but a friend of mine was doing well nursing, went on the regular pill for exactly the reasons you describe, and within a short time (a few months) her supply was gone. She is convinced it was the pill that did this, since she was only at the 3 month mark with her baby, was exclusively nursing, and should have had ample supply. For her next 2 babies, she did the mini-pill plus condoms for added peace of mind, and nursed both for a long time.
Knowing her experience, I did the mini-pill after my first and mirena after my second. My choices were based on my priorities at the time. After #1, I knew I wanted a second child, and while I preferred to have them a little further apart, an "oops" on the mini-pill would have been good news. After my second (which didn't happen until I quit taking the mini-pill), I knew I was done with babies and mirena is much more reliable than the mini-pill. Both times, my supply was great throughout, which was important to me.