Keep reading and talking to friends. You are on the right track. Arm yourself with as much knowledge as possible and you will learn a ton from your first grow. You are wise to start with a smaller initial grow. You can dial in the growing process and scale up after that.

As for plant height, this is very much strain dependent. Ask your friend how long he vegged his and how tall they grew. Some plants can double and even triple in size during flower. I suggest you anticipate doubling in size. So veg them to 1.5 feet and flip to flower - likely 3 to 4 weeks of growth. What happened to your initial idea of doing a scrog grow? Scrog allows you to easily control height without sacrificing the potential of the plant - bigger plant = bigger yield. It will also allow you to maximize yield for your space by giving all bud sites equal access to light. It takes about 2 weeks longer but is worth the effort. Once they half fill the screen you can flip to flower.

As when to drop them into the pots, I'm not a hydro grower so I can't really answer that. If it were soil you'd drop them into the pots as soon as the clones showed root growth of 1/2 to 1 inch.

You have ton of lighting. Not over kill but close. Your plants will do very with that coverage.