The only way to net a positive benefit from growing plants to feed plants is if you are growing them in the ground. Sure, legumes and other nitrogen fixers will assimilate nitrogen from the air, but all the rest of the nutrient accumulators need the nutrients to be present in the soil. It doesn't make much sense to buy nutrients, feed them to nutrient accumulating plant, then feed the nutrient accumulating plant to your indoor garden... All you are doing is unnecessarily shuffling nutrients around, not accumulating them from the earth. If you have land where you an plant things like comfrey and nettle straight in the soil, you will be reaping a positive benefit from their nutrient accumulating ability.