To answer a few of your questions, 1. I am not really sure about the stove pipe, but I would guess it would be OK, especially if you add more length to it, and have a good draft or forced air.
2. You could use the same method that he used, it would work fine, BUT you wouldn't have the best insulation and in the long run, the red brick adds a lot of extra weight onto the arch, possibly aging it a little faster. To cut down on weight, you can use several things under the traditional firebricks, I put ash in the back of arch, then cement board and then firebricks; the ash cuts down on the weight, while still adding good insulation and takes up the space to allow the least amount of room between the firebricks and my flues (less room between is better, forces more of the heat into the pans for better efficiency and evaporation rate.
3. Once again, the more insulation the better, it will increase your evaporation rate, cutting down on your boiling time. In my firebox, I used ceramic fiber blanket first, then the cement board (arch board) and then I put the thinner firebricks (using cement to hold them in place), with this combination you can put your hand on the side of my arch without getting burnt. Not all of this is needed, but in the long run it does save time and also wood. I would also recommend adding forced air if you don't already have it, at least under-fire, you will get a better boil in your front pans and all the way to the back of the flue pan.
Good luck.
2,000+ taps and growing
3'x12' Vortex, MAX flue, and steamaway
24'x48' timber frame sugarhouse