There are too many options. Transplant is typically in order if the roots are fully occupying the current container. You have to consider how long you want to veg your plants/how big you want them to be. You could let them grow for another month or longer before you transplant again and then force flowering, or do a final transplant now and start flower in a couple weeks, everything is up in the air. Also I assume you have to sex them, and determine which ones are the females?
You could use liquid organic nutrients (Earth Juice is a fine brand), or strictly raw materials such as compost, bone meal (or various other meals), fish fertilzer, kelp, manures or guano; you could brew actively aerated compost/casting/guano teas, or just load up the soil with organic amendments plenty of people seem to have success doing just that. Super soil and tea recipes to be found in the Organics forum and sub-forum.