Ebb-Flow size of root growth, choosing rockwool size

After many years of growing great in sunshine mix we have just aquired a top feeding ebb-flow setup, so it is time to learn a new growing method. I know the basics of the system really well but don't have the experience to know what to expect.

The table is about 4ftx4ft, and I am running it in a room about twice the size under 2 1000w bulbs, alongside other plants I'll be still growing in sunshine mix and grow bags. Ventilation and temp are great. I also have other rooms for differnt stages and cloning, but only one big enough for the table.
I'm curious about how much space the roots need in this medium. I already start my clone in small cubes. The plan was to block up and let them veg till 6"-8", then flip them over into flower. So I want to make sure I account how much space the roots need when deciding on rockwool sizes as well as how many to run on the table.
Which brings me to my next question of spacing in an ebb-flow system. I know they can grow closer togather but don't know how much space they will need without being crowded. I would rather give them a little extra and add more in future cycles it resouces and space are available.

I'm not a noob, and I have tried to seek out and research this information, but it seems like I need more personal insight than defined facts to help me find the right answer.