Sorry to say, but dragging around a simple chain harrow does not a work horse make, any horse can do that. Heck, my mini burro could do that. I'm talking actual, real working farm horses that have to do an actual real day's work.....the way drafts are bred and built to do.
How much experience with real working animals? Not puttering around the paddock, not driving a nice little cart around, but actually putting a plow in the ground and having them work for a living?