This looks like an excellent start. I am getting ready to do the same thing with a 3 gallon open circular bowl I bought at my LFS. I also have a 8g Walstad. I don't sift my organic soil or mineral it by baking it. It did produce tannins in the water for a couple of months. I had good plant growth right out the gate but noticed slower growth right around the 3 month mark. Pretty sure the soil is just inert at this point.
Good luck with the bowl!