The space needed can vary quite a lot depending on strain and how you grow the plant. It sounds like you'll probably be growing in some pots with soil, and want relatively big plants. In that case you'll need probably at least 200watts of quality CFLs to start with, then just add some in if your plants get big. When figuring the space needed, consider that the plants will probably need at least three feet to grow upwards, and you'll need to keep the lights from touching the plants, and the pots will take up some space as well. Plants will also like a few feet of width to stretch out.