1. Could be as some die off will happen on the liverock.
2. For a reef tank, I personally don't like crushed corals in the sump as they retain too much detritus. Some hang them so that it can be cleaned easily.
3. Yes becuase of increased light intensity.
4. Looks ok.
5. Best to use NSW. or if not try to use purified water with saltmix.
Try turbo snails, they are great in removing diatoms. But in time they will all be gone. Just do your regular water change and maintenance.