The example in the video looks like it might have benefited from some more room between the boats, as the prop wash might have been interfering with the righting of the tow.
Horsepower calculations? I don’t think there’s a documented formula, but The captain of the tow boat should be very confident that his craft can do the job before fastening to it, especially in open sea conditions as shown.
It’s always prudent to have a sharp knife handy in this line of work!