Hello, thanks for asking. You can grow in 7 gallon pots without any issues but it may be too much for an autoflower, so we recommend growing in 4 gallon or a maximum of 5 gallon pots so you don't waste space. You can definitely use iguana juice, just make sure you start with 1/3 or even 1/4 of the recommended dose to avoid nutrient burn, and as your plant grows, gradually increase the nutrient dose if you feel like your plant is hungry. As for the pH, it will depend on the substrate you're growing in and the specific nutrients so make sure you read the manufacturer's recommendations.