I'm doing some bartering which has allowed me to acquire a nice size growing room where I work. The room measures 14 feet wide x 20 feet long and the ceilings are 16 feet high. I also acquired several free 400 watt metal halide warehouse style lights that I will be utilizing. I have 12 at my disposal for 4800 watts of total light or 432,000 lumens. Now I need some help with layout and height..

I was originally going to use 9 lights (3 rows of 3) and mount them at 10 feet from ground to bottom of light. But I'm wondering if I should just use 12 (3 rows of 4) -- too much light isn't a problem right? And what height should I use? I'm going to have some tables in there with smaller plants (3 foot high tables or so) and then larger plants on the ground where the top of the plant could range from 2 feet to 6-7 feet high.

Thanks for the help!