For a 3x3 space, how much light is best? (and what type)

After a bit of trial and error, I have mapped out a grow spot about 36 inches wide by 36 inches tall. That said, here are my big questions:

1) What form of lighting would be most efficient in terms of power usage? I would like to keep my electric bill down as much as possible so as not to attract police attention, but nearly all the plants I'm growing love full sunlight.

2) What wattage would suit my small space the best? So far I've gotten answers ranging from a 100 watt CFL to a 1000 watt HPS lamp, so any clarification here would be great?

3) What form of lighting would be best for autoflowering strains?