Congrats on #21. I know who you purchased yours from because I asked them what available serial numbers they had and #21 was listed. They had a few early builds (double digits) and the rest were in the 700's. I tend to lean towards the later builds because it allows for kinks to get worked out, but I requested #21. They said it was mine, but I received one of the later builds in the 700's. Mine is still in the box because I've got to get it upstairs.
I read your post and my first thought was that it could have been me dealing with the flipper bolts, lose flipper. Glad you got it sorted!
Enjoy your AFMrLE!