Excellent post! As a potter (didn't build my kiln, but did the PID
controls), I can throw in a few more tips:

A common alternative to firebricks for a quick, homebuilt kiln is
ceramic fiber blanket (Kaowool or Inswool):
http://www.anvilfire.com/sales/k_index.htm
It's also sold in board form. The main disadvantage is that it
generates ceramic dust if not coated, so should only be used outdoors.
Or it can be coated w/ ITC. Use a brick or two for the floor.
http://www.anvilfire.com/sales/pages/ITC_index.htm
(Actually, I've seen pictures of a *plywood* kiln whose only insulation
was a thin inner coat of ITC. That stuff is amazing. Don't know how
hot it could go, though.)