I'm not sure what your goal is.
I'm wondering: do you want your horse responsive for everyday riding; or is your goal to influence the way he moves, which is quite a different thing. Working completely off your seat is very cool when riding; but it doesn't necessarily help in strengthening the topline or suppling the joints.
But keep in mind, with an arthritic horse, you have to make sure your therapeutic exercises do not become, in fact, harmful.
I'm also confused about the "higher steps." What's that all about?