What do you mean how do I clean? The normal way, wipe it down with a dishtowel and wipe it down again. Right side is raw side, left side is cooked side.
Also duck liver mousse, gizzard dressing. Duck comsomme, duck gelee.
For reheating it makes sense for me. For initial cooking it's all about getting the correct texture. A low slow sous vide cook will give you a different texture than a slow braise. But it takes a long time, like up to twelve hours.
Veal marrow bones are the best. The marrow bone is usually from the arm or the femur. Larger the better of course. :)
It's really simple, but in general, I don't think you can get the butcher to specifically get you those cuts. They normally come in a case of veal bones for stock and you just save the better ones.