Depends how much nutes are in ur soil. Strong soil u would wanna feed less with ur water. If using coco I would feed, feed, water. Or feed everytime and flush with straight water about every three weeks.
Make sure u give it full 24 hrs of light so it can revert back to veg. The best way would be to take ur cuttings before u induce flower an then by the time u have good healthy roots ur flowering plant should show it's sex.
How many plants? U can veg good with a lot less light then what u need to flower. As long as u have good air flow the 1k should not be to much. Make sure it's not two close to your plants. I recommend two ft min. And up to four feet away if needed. I veg under 400 mh and flower with a 1 k hps.
I recently jus started using seaweed extract for spraying. However I have used superthrive in the past. It should say drop-a-gal on the bottle. Follow that and u shouldn't burn them. 3-5 drops per spray bottle might be to much. Definately would rinse with straight pH water for day two. Also...