I'll start with the original post.
First thing that comes up is the metal stand. I just want to mention I work with metal for a living, and have training in structural welding. If this was not the case I would not have put my oven on a metal stand. Make sure that yourself or whoever fabricates the stand has the experience needed to make it safe. An oven collapse could easily kill some one, safety must be your first concern so build quality must be #1. Same goes for the casters, use only top quality industrial casters rated for the intended load.
As for insulation on top of the dome, traditional or not I would insulate the heck out of it. Even if you can confirm that traditional ovens have sand over top of them in place of insulation and insist on going this route(I wouldn't) I would still insulate well over top of the sand.
Now for the questions in your second post.
Tuff is a volcanic rock, much like pumice or scoria. It is light and full of air cavities, so it certainly insulates. From what I've seen it is formed into rough bricks and a layer is put under the cooking floor much like any other underfloor insulation. That said I have no clue where you would get it, and just don't think it would be worth the hassle. Insulation is insulation and I am sure modern insulators are just as good and probably even better.
I've never used FB board, but I do know it is made in asia and many people comment it is much softer then other insulating boards. You should be able to find cal sil board locally if you want to use a refractory board under the floor.
Vermiculite and Portland and Perlite and Portland will yield similar results. I personally like the Perlite a bit more but whatever is cheaper is the way to go. 4 inches thick is plenty, but if you want to go over kill 6 inches would be more then enough.
65mm should be plenty thick for the floor.
On to Craig's Acunto,
I've noticed in pictures it seems to be built different then a SF oven(the soldier bricks look to have their wide side facing in), and this sounds like another difference. SF has the specs for their ovens listed on their website. If you do the math the mobile oven has no space for insulation around the soldier once the brick thickness is factored in. The stationary oven does, but we are talking about a mobile oven. I tend to default to SF as the standard simply because it is the most documented and people all over the world rave about them so I assume they are a good representative. I have also read a quote from a famous italian pizza maker(can't remember who or find the quote like a dummy) that SF puts a secret mix of salt over the dome and it is the one part of the build he will not let anyone see. I'd love to hear everything you know about the insulation on your Acunto.
Think that is all for now...