If you chose to store the first runnings, make sure the wort was held at at mashout temps for long enough to denature the enzymes. If not, you'd end up with basically a 2+ hr mash on those first runnings. That would make your beer considerably dry. I say this from experience from my sytem about that. The first few times I tried this system, I was getting 85% attenuation from several different yeast strains, and it was way to dry for the styles I was trying. I traced it back to letting wort sit without being mashed out til the enzymes denatures. Now, I bring the wort to a boil before I let it sit any time.