Thanks for your replies. I have decided that rather than put bricks directly against the stove I would make a Gabion wall enclave for it. I already have the wire mesh to do it, and river rocks are free for the taking. (https://gabion1.co.nz/prices/
this is what are called Gabion walls in NZ) It will not touch the stove but will hopefully still absorb quite a bit of heat, and should give sufficient protection from the fire heat to the wall behind it.
I have also found someone in NZ that has a 130mm water jacket prototype sitting on the shelf that they will sell me for lest than half the cost of the Australian one. The first break in the stove pipe is 60cm / 2 feet up. I was thinking of putting the water jacket above this, and of putting rockwool insulation around the flue below this, as well as putting a piece of rockwool over the stovetop when I am not using it. Would doing this help increase the combustion of the stove, and would there be any danger in doing this to the stove?
The burn chamber itself is a 28cm diameter x 35cm high bucket, with a 6 cm diameter hole in the middle of the bottom of the bucket that sits on a 5cm hole through the bottom of the stove (with a damper there). Then it moves up and sideways under the stovetop to the chimney. The top airflow damper to the chimney on full is 3 x 6cm diameter holes, so the smallest point in the whole system is the 5cm hole at the bottom of the burn chamber. Because the round lids on the stove top are not sealed, you probably always get a small secondary airflow just before the flue, and could increase this by lifting a lid a bit.