I definitely recommend the addition of a yard (with an appropriate yard lead, that allows doubling a cut of cars from one track to another without fouling the main lines!) However... your latest design doesn't allow for comfortable reach to the yard area.
Another issue, a yard in the depicted location is not accessible. 3-rail O gauge couplers can't ever be expected to work properly. You have a huge space to work with, so don't be stingy about creating aisle(s) for the operators to stand in. My $.02.