FIrst off, I've read about chronic and it sounds like an awesome strain if you want to produce in mass!! 400 W HPS is ideal for 3x3 area. 600 W is ideal for 4.5 x 4.5 area.
If you want to harvest once every 4 weeks, you will need two flowering set ups, just like you mentioned. That is ofcourse assuming that the strains you are growing flowers in 8 weeks.
You mentioned all this stuff about buckets. If you want to do flood and drain the easiest way to do it is get a flood tray, resevoir, water pump, air pump, air stones, flood and drain kit. By using one tray, you are not flooding indavidual buckets, but just one whole tray that your pots sit inside. This is much simpler than connecting your water hose to all these different buckets; you just connect it to one tray.
Also, with the tray method you are not restricted to a certain number of plants to grow. YOu can stuff as many pots in the tray as humanly possible. Let me see if I can find you a post on how to build this.