palerider--first-off, props on your set-up! It looks first rate to me! Your last Q about changing nutes...the theory involved is that your going to all this effort to grow your weed as fast as possible(as opposed to soil). So you want to change nute solution often so that you ensure your not even slightly deficient in any nutrient. It's just another way to push your plants as hard as you can to get the very most from their genetic potential.
...my two cents