- Feed coal to both of them from a central coal double-chest by using hoppers that connect from the bottom of the coal chest to the side of the furnace.
- Feed the materials to cook in each furnace by using a hopper from an input chest to the top of the furnace.
- Drain the cooked output with a hopper from the bottom of the furnace into a cooked products chest.
Then put stacks of coal into the supply chest and whatever you want cooked in the supply chests.
Full auto furnace: The furnaces will keep cooking stack after stack so long as you are close enough to keep the chunk loaded, you don't run out of coal, and you still have something pending to cook in the supply chests.
It's a very small build, which is absolutely fine. It's going to seriously constrain your block choices and limit any potential technical builds, which is sometimes fun trying to overcome.
My advice would be to try to do something that you wouldn't think is possible in a space that size. For example, and only if you want a real technical challenge, you could try your hand at a shulker-based storage system with all of the redstone and actual storage hidden underground, with the above-ground footprint just an input and output where your filled/empty shulker boxes go.
But if something like that sounds too complicated, my overall suggestion still stands: just try to do something that seems impossible in that space at first blush. It doesn't have to be technical. Decorating small spaces like that is enough of a challenge!