laying cooking floor

[SteveC]

Hi, I could use some advice on how to lay the oven floor and stuff. I've built my base, following the basic FB instructions - breeze block structure, topped by a slab of 4 inches reinforced concrete, then 4 inches vermiculite concrete. Local advice didn't like the idea of a simple 5:1 vermiculite:cement, so the top layer is more 3 vermic:2 sand/gravel:1 cement. I'm thinking of putting a 2" insulation board on top and then build the oven on that, to increase the insulation before laying the oven floor. For the oven itself I'm sort of following Russell Jeavons for a 1100mm inside diameter oven, not cutting the oven floor so it fits inside the walls of the oven, but laying the floor over the whole slab and then building the oven on top of it. I'm just going for a straight igloo type; no chimney. I've had the metal basher make up the tool, and the arch for the opening. I've many questions, the first of which are:
1. Is that a good idea for the 2" insulation board? Will it stand the weight of the oven over time or will the oven walls start to press it down and collapse it??
2. For the floor, my plan is a layer of some really heavy and solid engineering bricks that I can get here, and then a layer of large, almost 8" square, 1" thick quarry tiles over that (nice size and smooth top). But how should I lay these? Russell says he uses 2 layers of clay pavers and butt joints them (ie no mortar between them), but:
(a) for the bricks, should they be laid on a bed of mortar, or should I just lay them loose on a thin bed of sand (say) directly on the insulation board; or maybe they should be mortared in, not butt jointed?
(b) same for the quarry tiles - should I lay them on a bed of mortar, or just loose on a bed of sand on the bricks?
3. For the dome, the tool only works for so many layers. Then Russell says make up a weak mortar dome, and use it to support the bricks while you lay the final courses. I can see this all going horribly wrong, and am starting to loose my nerve... Any tips/confidence inducing experiences??
Be very grateful for any tips/experience.
Thanks.