It may depend on where in MD you are, but I’ve boarded in both central MD and currently AA county. Mine is a TB who generally gets fully clipped, or a hunter clip, for the winter. Even then, it is rare that she needs a heavy–maybe a week or so each winter. If you’re not planning on clipping fully, I wouldn’t bother with a heavy.
What I would start with is a no-fill sheet with an extended neck, and a medium weight with a detachable neck cover/hood that you can put on or take off depending on temps and weather conditions. See how the horse does with that, and you can add to the wardrobe if you need to, and what clipping you end up doing on the horse depending on its work load.