with 2000w and that aero setup I wouldn't top at all just get a crop of clones ready, fill every whole, flower, chop & repeat

I don't know much about those big grows but with my aero grow I've found the lower the ph I use the lower the ppm the plants want...the higher the acidity the quicker they get the nutes or easier or something it's in the faqs somewhere

I think the idea is about 500ppm veg and 800-900 for flower and 1000 at the very end....ph always between 5.2-5.5...I'm sure there is a little change depending on the strain and all that but just keep a ton of air moving through the room if yer gonna grow that many plants and you should be fine...what sorta things are you iffy about I can help better if you just post a few questions