I would flush with a weak nutrient solution.........then start feeding twice a day to substantial run off with a pH around 6.0.
Lower your EC to around 1.0 to 1.5 at the most.
Never give plain water and never let the coco dry.
I don't recommend mixing coco with soil...........they have different pH requirements and different watering/feeding requirements. Coco should stay saturated and soil needs a wet/dry cycle.
Good luck and welcome to RIU.
Most auto growers transplant........even Mephisto, who only sells autos, recommends starting in solo cups and transplanting.
I start my seeds in a solo cup in a 50/50 coco/Perlite mix and transplant after 2 weeks from sprout.
When they look like this.
I start feeding to run off around 3-4 days...