Hi April, I have found the 4” vortex to run fine without any secondary air, there is a slight temperature difference but that is probably a good thing in my case!
It also runs well without a door but it burns out very quickly that way so I would recommend a door.
Yes you can control the fire by restricting the air but then you will quite likely get smoke on the viewing glass and out of the chimney.
I found that by using the BBQ cast iron under the ceramic glass the cooking temps are just about right, around 350-400c at peak burn but mainly around 250-300c.
To be honest compared to a electric or gas stove or oven, rocket stoves are nowhere as easy to cook on, they are designed to burn hot and fast, perfect for heating a mass but a bit volatile for cooking!
However with my outdoor vortex stove the surrounding bricks and granite worktop get lovely and warn.
The vermiculite board is still looking fine, no noticeable Deterioration so far but I dont expect it to last for ever.
In my case, if the board fails after a couple of years I can just replace the whole unit for £150 and a couple of hours work.