You got a while to go buddy, just dont get impatient and cut early. You have a long time to go, and even when you think they stopped growing and they are done, they are still filling up, and putting on potency. Get a 30x lens or something so that you can see the trichomes so that you make sure you harvest at the perfect time.
Fox farm has a very good nutrient line, If you can get some I deffently would.
However make sure you dont burn the plants by adding to much nutes, doing this in the flowering phase will greatly reduce your yeild. Depending on what brand of nutes you get, start at 50% or under, and see how the plant does with that.
best of luck to ya mate <3