Hello deadhead. I'm not so familiar with the ferts you are using such as superthrive but I assume they are all organic. Foxfarm is a great soil to use, I use a similar soil called happy frog for my plants and they love it. Earthworm castings, bat guano, mushroom compost, perlite are all great additives to your soil. 150 watt HPS will suffice if you are only flowering I'd say 4 or fewer plants. I use a 400W HPS in each of my flowering rooms for around 12 plants in each. HPS is only used for flowering because of the light spectrum it emphasizes (redish-orange) while fluorescents or Metal Halide are best for vegging with the blue spectrum.

For organic gardening you really want to enrich the soil as much as possible so any "fertilizing" in just supplementary. Peace of Mind has several great soil additives that you also use as top-dressing twice in flowering. The two I use are "fruit & flower" and bat guano.

Hope this helps. Let me know if you have any other questions.