1) I understand buying off the shelf parts for your prototype. But spending hundreds of dollars to be shipped parts I could have bought myself is just adding more middle-men into the supply chain. At this point, just sell the parts list and plans for $20. And when you have built parts with ease of assembly in mind, so this is 5x easier than DIY with parts from home depot... THEN sell the kit.
2) You need to share data of how much water is needed on an ongoing basis, in different climates. People in Arizona with limited water supplies might not have the same resources to put in, for example.
3) You need to talk specifically about what plants work well, what the yields are,in different climates and growing zones, and recommend planting strategies for different locations.