that is the most awesome coop.. the weathered wood just adds to it.. i would leave it and stain it anyways.. the mold is a must to get rid of wear masks when you do it.. you might want to use bleach to kill it and look where the water is coming in..maybe caulk it for the time being. you do need vents that you can close. we just cut rectangles in the wall and used some left over hardware cloth then put a hinge on a piece of wood for the cold windy nights so we could close them, other wise they can stay open. you can mix 1/4 bleach to 3/4 water and spray it on the mold. good luck with your new beginnings i love it.