While it is true that a plants root system are often bigger in soil where they need to search out water and
nutrients. You'll be surprised how big the plants root systems get in hydroponics when you actually see them. So don't under estimate how big the root mass will get. Personally I would never grow tomato's in tubing (unless it was at least 6 inch wide, and the plants spaced 5 feet or so apart), 5 gallon buckets each minimum. Small or determinate peppers, I would give them 3 gallons of root space each minimum. You can always grow how you want. No mater what you do, it will be a learning experience. I have a plan to grow small (3-4 foot tall) corn plants in NFT rows, but I need to do some testing to check spacing and root mass needs first.
I attached a picture of the root mass in a similar system I built years ago. That root mass was from 4 pea plants growing in flood and drain system with 4 inch wide ADS tubing.