Hi Bob
If your system drains quickly then I would water every 20 to 30 minutes. I think some members are having problems with over watering their plants. That is why a cycle timer is important. The plant roots don't need to sit in water to get
nutrients. When the cups drain fresh oxygen is suck into the medium to the roots.
If your hood doesn't have glass then 24 inches for young plants and about 16 inches as they get older.
That's the reason I use solo cups so I can spin and move my plants around the garden so they get equal light.
Just fill the container enough to last about two weeks and then you won't have to throw to much out when you fix up a new batch.
Ron