Go for width IMO.. you can use techniques like Low Stress Training (LST) or Supercropping to control the hieght.. and more width will allow you to have more plants on the floor. Most of the guys I know that grow well use Sunshine Mix #4 for their soil... it has the perfect pH for growing Cannabis. You would be best to start out with a tried and tested 3 part nutrient system. They can be found at any hydroponic store, and some year round nursery's will carry them as well. I would recommend General Hydroponics Flora Series as it is the cheapest and gives you everything your plants need. The website has simple feeding scheduals you can use to start out. Cannabis can handle a LOT more than what they recommend in optimum conditions.. but their formula will give you healthy plants and a useable end result. I would also recommend using a seaweed extract like Growth Plus as a foilar spray. Mist your plants with it every day right when your lights come on.. It will help with mold and mildew.. and you will notice a BIG difference in growth if you spray vs not spray.. The stuff works awesome.. I highly recommend! Check out my thread http://boards.cannabis.com/basic-gro...w-attempt.html it outlines a grow that I am helping a friend of mine through. Its a much larger scale than what you have, but there are a lot of good tidbits for new growers... This is only his second crop! Good luck!