1. I bought high temp wool insulation from Axner - if you have a local supplier of kilns and kiln furniture, they may supply it as well http://www.axner.com/superwoolfiber-1thicksoldpersqft.aspx
2 In a pm, I suggested hinges at the top because I screwed up. Hinges should be at the bottom. The best way to do it would be to build a bracket at each side, locate the pivot point of the hinge as far from the front of the oven as possible so that the door will stay closed without the need of any catch, and then if you want a a stop system so the door will stay horizontal when opened, work that into the bracket. That is the method used on my latest oven - the outer bolt is the pivot point for the door - the inner one rides in a slot that stops the door at horizontal when open. photos are below.
3, Scott likes the burners to glow red or orange - I am on the fence. In my prior ovens, they did not glow - in my current one, in which I replaced the element with a higher wattage broil element it glows a very bright orange - the problem is that I have had trouble with burning the cheese on a 2 to 2 1/2 minute bake. While the thermocouple for the oven may be set to 600 degrees, it takes a while for it to sense the temperature - and the broil element is well over 800 - which is giving me very fast bake times - but in some ways too much heat. So my long answer, if you get the surface brown in a time that works for you, don't worry about the color of the element
4 I don't know. The thicker the stone, the more thermal mass you have. Some suggest you get a thick stone, they say the temperature will drop less with each pie that comes off the stone than a thinner stone - which is true. My question is how long will it take to reheat the entire stone back up once it has dropped to a temperature that you think is too low to use, and at that point, wouldn't a thinner stone reheat quicker. On top of this issue, you have distance from the upper element - the closer to the upper element, the more browning you will get in the same time, and for the time that there is no pie in the oven, the upper element will be putting a little more heat into the top of the stone than if the stone was thinner and a little further away. You are only talking about a 1/8 inch difference - though it will be 20% thicker - I would probably go with thicker - but if it is much cheaper in shipping charges, I think you would be happy with the 5/8