Those aren't organic-specific questions.
Wattage isn't as important as usable lumen output. You need a minimum number of lumens per square foot to grow healthy plants. For example a HPS400 can light a 3x3 area of floor space, while a HPS1000 will be good for a 5x5 foot square.
Sounds like you have a bit of reading to do; start with the Grow FAQs section and the sticky at the top of the Basic section.