Grow / Veg room yield/light question help please

I need help. I am starting my second grow op, and i now have a nice amount of space to set it up. What i am still debating is how many plants and what kind of lights would be more energy efficient and money saving while still putting out enough light for my plants to grow. I don't want to be using too strong a light than needed and wasting money. I have a room about 7x7 for flowering and a nice sized veg room. My plan is to veg six flowers, or maybe more, and flower the same amount at the same time in the bigger room. Can I use a 400w to veg if i have more than 6 plants? or would a 600 be ideal? Also, for the 7x7 room should i just run a 1000w or could a 600w pull it off....this is probably depending on the amount of plants as well but right now I am thinking six unless I could profit more off filling the room with more plants. Not sure if more plants in a tighter area would yield more than 6 plants in the 7x7 room. I am really looking for suggestions and tips on how I can yield the most bud with the space I have. Was going to grow in soil as well. Or would constructing a hydro system be better? Thanks in advance for your help guys. This site rules and everyone here is such a great help.