I've never tried hydroponic so I can't speak from personal experience, I've only read in a few different publications to give soil growing a try first to get a feel for it. I'm on my fourth grow and I THINK I finally am getting it right but I can already see I've made a few mistakes even with this grow. It's not as hard as some people may lead you to believe but it's not as easy as others may think. 400W for four plants should be plenty, you'll need to consider removing the heat from your grow area though. Another option is LED lights which produce little to no heat and are much less expensive to operate and will last many times over longer then HPS however your initial cost is higher.