From past experince i do find that soil would be better. But i was thinking about using a 6x6 rockwool at first then when the roots come out i'll transplant them over to a 5gal soil pot. This is so that they can get the fast growth with the rockwool and once their big enough i have the advantage of soil. Would this be fine?

I'm not much of a soil grower, what soil do i use?