That floro will be fine. A 400w will do five plants. You could technically use the HPS for the beginning too if you want to save money on equipment. For the seedling stage you could use CFL's or a workshop light. I've seen people use them right from the beginning though too. Might be something to consider especially if you need a nice exhaustion/odor control system for the 400 watter.
GL, :jointsmile: Bree