I agree that there are a lot of issues that need clarification right now, and it's simply poor form for there to be so many unanswered questions.

Just a couple of things - because I'm able to accomodate automatic postage discounts, the FVF on shipping is being charged on what the buyer pays, not the total of separate postage amounts (and I can only presume that will be the case where an invoice is issued prior to payment).

I've had a couple of purchases now where the buyer bought from listings created prior to the 6th, and some that were created or rolled over after, and the FVF has only been on a percentage of the shipping. (For example, 5 items where only one is eligible to be charged FVF, the postage charged was divided by 5 and the FVF percentage was charged on one fifth). 

The system for overpayments / FVF  etc for individual payments sounds like a PITA, I have on all my listings that separate payments = separate packages, but I will issue an overpayment refund and combine in some circumstances. Not sure how I'll go about that yet.