First time using autopots, 100% clay pebble grow?

Hi guy I'm looking for some advice.

This is my 2nd grow and my first time venturing away from soil. I want to get away from soil as I found it messy, and also in my area it attracted a lot of gnats(tiny flies) in the damp soil which I could not get rid of. So I'm hoping to move to something cleaner/easier and also a bit more predictable.

I have gone and bought a DR 240w and an 8 pot 15L autopot system with airdomes running from a 100L reservoir. At the moment I have a 600w HPS with a parabolic reflector, I'll be getting another 600w in the future as the plants grow.

I've already bought 3 50L bags of Canna clay pebbles and Canna Aqua Vega/Flores, Rizo and Blom boost.

I have 2 Holland's hope and 2 Big Bud Germinating in some tissue right now along with some clones of New Purple Power in rockwool in a cloning box. I don't plan on moving anything into the autos fr another 2-3 weeks but I'd like to get everything set up now while I'm waiting.

I have a few questions, any help is greatly appreciated.

1. What medium is best for Autopots? I would love to use 100% clay pebbles as they are clean, mostly sterile and reusable. However I'm looking for maximum yield here and also I'm well aware of my NOOB skill set so I don't want to use something that is to unforgiving. Coco maybe? Soil/Perlite does get a lot of big-ups too. What are you guys using in your Autopots?

2. With the reservoir I want to put in an airstone, is there any particular size I should be looking for?

3. With the Airdomes what size air pump should i be looking at to run the 8 airdomes and the reservoir?

4. Do I need any other nutrients/ additives other than what I've got above? I 'd rather have stuff on hand just incase!

Thats it really, I'm quite excited my first grow was initially going to be outdoors but crap summer forced it into an ensuite. The plants grew big (to big over 6 foot) and by the time my grow tent came they plants had gone into bad health from being in veg too long and getting root bound, along with bad watering on my part. I'm hoping to do it all right this time round.

Thanks again.