fill your pots all the way next time, your just wasting what could of been valuable root space. the size of the root system greatlly effects the size of the canopy. I'd transplant now, more root space is always a good thing. bury it so the bottom 2 leaves are about a 1/2 an inch above the soil level in the new pot.
24/0 is fine, to start flowering you will need to go to 12/12 unless you get an autoflowering strain.