I think the issue with a rocket mass boiler is always going to be the heat up time--the real key is the heat retention times. With an insulated
water container, you can have
hot water temps for long periods without needing to burn. Then, once that water starts to cool down, you have warm water to heat up rather than cold keeping your burn time nice and low.
Thomas has already mentioned that 3000F is not going to be achieved. I did a quick search for that number of Peter's and it is closer to 2200F.
Rockets are not "double burners"--they use a primary air for initial combustion and a secondary air port to inject oxygen into the hottest point of the stove to create greater combustion. Keep looking through permies, it has a search function that works well, and keep asking questions--we will keep answering them.