Never let it dry completely out, it should always at least be a tiny bit moist before the next flooding. This keeps the pH from crashing and the nutrient strength from spiking, both which will cause root rot.
Keep the rockwool less than 75F? Not sure, but I believe there's a max temp rockwool can handle before heat related root damage begins.
Keep your feed low. The more floodings you have each day, the lower the nutrient strength should be.