OP, addressing your first point... you won't need to pay the FVF if you cancel the sale with the reason "Buyer hasn't paid".

Quoting:

❝If the buyer still hasn't paid 4 calendar days after the listing ended, you can cancel the order by selecting the Cancel order button below and choosing Buyer hasn't paid in the drop down menu.

If you've sent a combined invoice, you'll be able to cancel the order 4 or more calendar days after the date the invoice was sent to the buyer.

Cancel order

Once you cancel the order, your item will be relisted automatically if it was a single quantity, Buy It Now item, unless you choose not to relist. We'll also remove any Feedback left by the buyer.❞

- https://www.ebay.com.au/help/selling/getting-paid/resolving-unpaid-items-buyers?id=4137

I'll add that you SHOULD NOT send a reminder invoice. The 4 days will restart if you do, so just let the eBay communication to the buyer do the talking. Four days later, the option to cancel with the "Buyer hasn't paid" reason will appear. Cancel with that reason, and the buyer will receive an invisible NPB strike. Sellers who have their Buyer Requirements set up properly (to excluse buyers who have 2 or more NPB strikes) will be automatically blocking such buyers, so this will hurt the non-paying-bidder/buyer.