In the past I have used coco, fox farms and a commerical brand unigrow organic potting soil. the coco and fox farms ran about $20 a bag, the unigrow was about $8.00. I didn't notice much of a difference between the 3.

As for ferts I have used miracle grow plant food, dyna grow, fish emulsion, peters, and schultz plant food. My preference is peters or schultz and the fish emulsion for vegative growth. for flowering I use dyna bloom and molasses.

As for how often to fertilze, the best advice I can give you is the less the better. But its important to watch the plants and adjust as necessary