Here's the latest progress on this. I've suddenly realised that I don't really have much time to do this - just less than three months. It will be interesting to see if I can finish it in time.
I've finished the outside border row and started on the inside. I have decided to only use one thread from now on - the outside row was too chunky and just didn't sit right, so I thought I'd try a single strand and it looks much better so far. I'm going to leave the outside row as it is - after all it is the outside row and all the way around so it shouldn't look wrong.