You should try some hydroponics yourself! I think it will quickly fill in some of your questions and give you a concrete understanding of the challenges.
Short answer: Soil and sun do a lot, replacing them requires many inputs and sensors
It's on my to-do list. I could see the need for light and moisture sensors, as well as nutrient bath flow sensors. Not sure what all else besides temperature and humidity.
Short answer: Soil and sun do a lot, replacing them requires many inputs and sensors