Some great ideas there thanks William!
I do like the idea of using glass bottles in a window. I have some I dug up from the old waste pit and it would be pretty cool to be able to use those. Useful threads:
https://permies.com/t/3486/cutting-glass-bottle
https://permies.com/t/40/11155/dirt-glass-bottle-walls
It also occurs to me that I am building a forge....so may be able to melt glass into a specific window shape.
As regards the flue temperature, I'm toying with the idea of a stone bell, which would extract some of the heat. I'm also not sure what flue I have, or will use. I might have some double wall flue, but it seems extravagant to use that for this. It is also not impossible I might still try for a stone chimney through the wall.
Christopher, I suspect that some sort of dormer/frame over the door will be the easiest option for the door height. I have a step at the doorway in my pallet shed, and it is a bit annoying to have the change in height. Also could be a bit dangerous, if someone forgets it is there, as a trip might send someone down the hillside.
Jay, rain can fall horizontally here pretty often! A hat is a good idea for stopping the rain falling down the chimney rather than spark arresting

. I suspect we can find something suitable, or if I go for a stone chimney, then maybe some tilted paving slabs might work as a cap.