Forum / Questions on Cordierite stones for DIY wood fired oven

Hello folks, I'm planning to build a really simple brick stacks of wood fired oven. I'm about to start a small pizza business around the neighborhood. I'm young and I don't have experience with building and concete materials. If you are experienced, please give me some advice..

The oven will be a simple one, using 4 levels bricks for the base with air pocket vent on the back, then the base for the pizza will be using a cordierite stone, and the top will be a slaps of bricks/fire bricks concrete/cordierite.. I will use mortar in between the bricks, and probably layer the sides with vermiculite..

For the cordierite though, the store have 2 types of thickness (1/2 inch and 1nch).

My questions are:

**Pls check this video for the imagery type of the oven:

1. Is the 1/2inch stone will be enough to resist the direct fire from the oven? will the thicker stone needed for a better result? I have tight budget and the thicker stone is almost 2x the price of the 1/2inch..

2. Is it necessary to coat the outer sides of the oven with vermiculite for a better result?

3. **Pls check the video in the link

Can anyone tells me why is the base of the pizza burnt a lot? is it too much wood for the fire? is it because the brick is bad?

What will happened if i use a cordierite stone for this type of oven? will it tend to burnt as well?

I'm planning to build a slightly bigger version of that oven, probably a brick more on the length and 2 bricks more on the depth(width)

That guy on the vid only have 1 brick for the vent, i'm planning to have 2 bricks for the oven vent, in hoping that the bigger gap will helps the oven have a better air circulation, so heats will be distributed more evenly.. Pls correct me if im wrong..

And for the depth(width), i'm planning to have it wider, probably 1.5-2bricks deeper so that the fire won't have direct contact with the pizza. 

My questions are, if i put 2 bricks gap for the vent, will it combust the pizza even more? or the indirect contact from the depth will save it from burning?