I dont know about the book, I have been thinking about getting that myself wbw... But decided not to,l just because I wanted to pick up on A7's Lite-c (which structurally can be done in a completely different way... read: CAN be).
I guess if you have no 3DGS knowledge yet, it'll definatly get you started, and it might be worth buying... but that's me, better wait for someone else's opinion on that too
about your 2nd question: "Is there a document somewhere that lays out all the differences between A6 and A7 and shows how to do the equivalent thing in A7 that is shown in say an A6 based tutorial?"
Read the AUM (acknex user magazine). it contains a small piece that explains the main differences between A6 and A7 in terms of major script enhancements.
good luck and welcome to the wonderfull world of scripting
!