Questions about starting build and idea with beer fridge.

I've been working through lockdown to get the base unit ready, and am suddenly finding myself ready to build the dome. Exciting but now I realise I have questions before it's too late.

1) Most urgent (given I'm planning to do this on Saturday) is whether there is a reason not to put a 20mm layer of vermiculite concrete under JUST the 50mm of CalSil board? Having it helps with my measurements and also gives a route in for a thermocouple probe later.
I plan not to put vermiculite over the whole oven 100mm slab, just some tiles to match the patio, to try and improve the appearance by making it a slimmer slab.

2) Following on from this, I plan to have the landing area within the outer tunnel at the level of the main slab, rather than extend the oven floor out all the way to the end of the tunnel.
I'm wondering if this will make it difficult to slide pizzas or perhaps larger baking dishes in and out?

3) The oven floor is 32" diameter. I have calculated the angles for my chains (before seeing the IT spreadsheet) and wanted to end up with the height slightly lower than a hemisphere - to make for more of a Neopolitan style, and again so it doesn't "look too big".
To do this I'm planning on having a chains 2,3,4 and 5 tilting at an angle of 15 degrees relative to the previous chain, and then chains 6,7,8,9 at a shallower angle of 7.5 degrees. That way less height is gained by the early chains.
The question is whether this is a bad idea - either due to having 2 different degrees of tilt, or due to 15 degrees being too much for one chain? (I calculate there would be a 30mm gap at the outer diameter between chains).

I'll attach photos/Google sketchup plans showing more detail.

Also, to give something back to the forum, I'm hoping that my base unit is a good idea (with no unforseen problems). The layout creates 2 small cupboards, one for a beer fridge, and 2 storage areas for wood. Also a small diagonal shelf for storing the long pizza cooking tool, which I read is hard to store. I'm hoping it will give better support for the slab too.

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