Advice with grodan

My last grow, also my first, was in 20 5 gallon buckets with hydroton rocks as the growing medium.
I yielded ~5lbs with that grow. Not sure if this amount of yield is good or bad (10x600w air cooled w/ top feed drip in a 12'x24'x7' room)

I'm looking to improve and am thinking of using 4, 4'x8' trays with 6"x6"x6" grodan blocks.
Perhaps have a net a foot or so below the lights to do Scrog.
I'm still a newbie so I need to know what the standard growing conditions are for grodan blocks.
I've seen that slabs have been put underneath the 6x6x6 for more root production.
Can use the hydroton i have from my previous grow instead?
How large should should the plants be before switching to blooming, and how many plants for each 4'x8' tray.
I'll probably stick to top feed with a drain back to the reservoir.
How often should I be watering?
Is this switch worth my extra money, or should I stick to my 5 gallon buckets.
I'm looking for the switch due to leaks in my buckets drain and Electricity costs due to long vegging. With 20 buckets, that's 20 separate drains to possibly leak. I'm looking to keep the room only as a flower room and create cheap vegging grow tent with reflective foam insulation.

Thanks in advance.
 
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