Bro, very nice technique! Throw a fan up directed at your lower third from slightly above. That constant slow breeze will keep it dry but not too dry. No moisture, no mold :)
You don't. Covering them up so they don't get light is the best way, but you'll probably see a bit of green growth on the cubes. Rapid rooter cubes are better in my opinion and dry out but don't have the same mold problems.