Waterfarms are cool. Good choice.

Waterfarm works by pumping air into a lift tube- the bubbles entrap water as they rise, pushing it up into the drip ring. Quite elegant really- the air entrapment oxygenates the nute on the way up, and then it drips down in a thin film over the hydroton. Plenty of o2.

I'd only do one plant per unit- but that's just rule of thumb. I like to do everything in individual cells, so that I don't have to deal with root systems intertwining. Doubly so if you're starting seed, as you're bound to see a boy. If you want to do more, you'll need to use a 'zyme product to deal w/ whatever's in there.
While it is possible to pull a plant out of hydroton roots and all, it does a lot of mechanical damage to the roots of plants left behind. There's no real physical resistance, it's not like soil- so it's real tempting... but man, what a mistake...
All those little abrasive balls, with a little bit of weight on them, spinning and grinding-

Ouch.

NL oughtta go bout 8 for most folk, but at that light level, maybe a little long?