Hi Pentlebay and welcome to the board. I'm sure someone will officially welcome you shortly.

In terms of the redemption availability, they tend to open up c.355 days out and with the limited seats per flight they are snapped up pretty quickly, especially at peak holiday times.

I was on the phone to the call centre to snag my LHR-SYD F tickets with Avios the morning they opened up.

Might be worth amending your destination or perhaps looking to use miles and cash with another OW carrier if your dates and destination are set in stone (although your Amex voucher wouldn't be of use for that booking).

Good luck finding something