From my research: the whole thing is theoretically water-only, but you might need some outside nutes/teas during mid to late flower or if you see deficiencies.
You veg in the container, minimum 7 gallons. The container has anywhere from 25% to 100% supersoil in the bottom; regular, good quality soil on the top. I'm going to do my first round with 50% super soil. That seems to be kinda the average amount.