Excellent work! Don't want to pile on because the overall work is excellent; but starting with focus on the first element in the form and the jumping to the first error both break accessibility rules. As a sighted user, I love them, but when I was doing accessibility work it was one of the things we had to remove from the site to be fully compliant.

A lot of your other items take view-ability into account are very much required for accessibility, so you may want to caveat those two items.