A 400 watt HID will cover a 3x4 space (idealy), the # of plants you put under that is a personal preference type of thing. I would put 8-12 plants in 2 gallon pots
okay....organics are simple, and even more simple if your using reverse osmosis water (no pH issues).
Here is what you'll need:
Medium = Fox Farm's Ocean Forest (some people use perlite with this if they are having problems with the soil drying out quick enough)...I use pure FFOF.
Fertlizers = Earthworm castings, Seabird Guano (high in N), Bat Guano (high in P), kelp Meal (algamin) or liquid seaweed, and molasses, and a bottle of cal./mag.
About your medium : The FFOF has plenty of fertlizer in it, so, you'll not need to fertilize for a month once planted into pot. Also, the FFOF isn't for young seedlings, it can be too strong. Fox Farm suggest using their, "Happy Frog" for the first couple of weeks of veg for the young ones.
About your fertilizers : A good way to use these fertlizers that I mention is to make a tea. To make a tea, you'll need a straining net. I found mine at a paint store. You mix your fertilizers together and put inside the straining net. You then place a bubble stone UNDER the net/fertilizer. Let this bubble for 24-48 hours. You don't want to feed your plants this pure. You'll want to add cups of your tea to new water. To give you an idea (example: during bloom, in week #3, I put 2 cups of this tea into each gallon of water). How much to use, is again, personal preference. Also, if your using reverse osmosis water, you'll want to add 1 - 2 ml of cal./mag. to each gallon, to all water and tea.
How I've done it?
I've taken my clones form an ezcloner after they have established a good root system and planted straight into FFOF (16oz. cups) and let grow for 3 weeks under flos.
Then, I transplant into 1 gallon bags of freash FFOF. I start my tea feeding the end of week 3 then only feed once weekly afterward except for the last 2 week to allow a flushing. You'll want to slowly back up off of the Seabird guano to lower the N in your soil, by week 5 stop the seabird guano and worm castings.
...I maybe getting you confused a little, and before I go any further, I just want to know if your following me. Follow me?