A: You can’t play more than All, so if you are getting a Bonus to your plays-per-turn, you still just Play All. Andy compares Play All to a sort of “Play Infinity” where, if you add 1 to infinity, it’s still just infinity. If you add 1 to “all” it’s still just “all.”
The existence of Play All Plus 1 does mess with this analogy, but note that the extra 1 card you play with Play All Plus 1 is essentially a Mystery Play, and, as such isn’t really part of the “all cards in your hand” which is what Play All refers to.