Nice design. I also like sand. Easy to clean. You can wet it down during the hot months and not worry about mold. My chickens prefer it. You can always put shavings over the sand. Something you didn't mention, which is very important is to put wire down under the perimeter of the coop. This will prevent predators from digging in. Take about a 4 foot width of wire fencing and place it so that 2 feet is around the outside of the coop and 2 feet is around the inside. I don't use drop boards but like the idea.
I think it depends on the weather in your specific area. The openings on all my shelters and coops face east, because rain and wind never come from the east here. We get horrible cold north winds here, so opening on the north side only work well in the hot months. Rain usually comes from the south here and sun is worst on the west side. Our designs reflect that, so figure out what the weather does in your region. I agree about the ventilation and that one side can be mostly open (hardware cloth covered), except for about 2 feet from the bottom, again to prevent predators.