Keep doing what you've been doing. You're encouraging some great root development by watering only when they need it and letting them dry out on the surface. The FFOF has really given your girls what they need. When you start using your nutes go very light because your plants are already in a well amended organic soil. I'd start out 1/3 to 1/2 strength and watch for any signs of slight burn on the leaf tips of the new emerging leaves. If you don't see *any* burn then you can slowly increase the nute strength. I like to do a routine of feeding them nutes every 3rd watering, always letting them dry out thoroughly before the next water or nute application. They won't need much during veg growth since you're in that bangin' soil mix... Once they get larger and you flower them you'll be able to water them every 2-3 days depending on what size pots you use and you'll still maintain giving nutes every 3rd watering... With organic soil all it takes is a gentle push from the nute bottle to get dank results and if you overfeed your plants it can slow growth and inhibit flower dank... 
