I don't know your strain, so any kind of yield guess is just that a guess. Are they feminized seeds? If not you may get males, which are no good for flowering.

But IF you got all 3 girls, put em to flower as soon as they are sexed. Yes, you'd have a quicker turn around, but less yield per plant,... so you do 3 plants in 3 months start to finish and get .5oz per, so 1.5oz total. Then start a new batch and get the same results another 3 months later.

Or do a single plant, vege it for 2 months while bending it down and training it to keep all the resulting tops even with the light. flower it for the 2-3 months it's gonna take and pull 1.5-2 oz off of that single plant. Do some searches for SCROG (Screen Of Green) style growing.

Yeah, get a way to monitor your PH, and keep inbound water 6-6.5 for the entire life cycle of the plant.

I use Ocean Forest soil, but plenty of guy's get away with the MG soil fine.