Wow! Great progress.
I’m less sure about the railway grass paper - the following is based on using it a few years ago, so there is a chance it has improved, but given how long it has been around as a product, I doubt it. I’ve found the railway flock paper rather stiff, but also prone to tearing, and it tends to be very mono chrome. I’d perhaps suggest a paper mache layer to give some strength and hide the MDF joins, then sand and flock - as then you can then vary the colours and coverage.