Rockstar, you want to decide basically if you want to go with an organic route or not, the a+b nutes will kill off a good deal of the microbes that are benifical to the plant, however you will get some minerals and other things from the compost that will help it....
I think you said you were in a desert like area, right? if you can find any seldom traveled spots that have water sources near them that would be your best bet, cannabis is demanding and will require your immediate attention in a desert like climate, im afraid, its easier to do obviously outdoors when you can just look in your backyard, even in desert, but guerilla in that situation will be tough and obviously hopefully you are planting now and not any later, i am not sure about how this would all work, but it seems to me since coco holds more water than just about any other medium therefore saving you water trips