YOur pony would easily be able to pull a trap and you and another adult, where I work we do driving for disabled so that involves an 11.2 pony, trap, me, and a person in a wheelchair that usually has feeding equipment etc. If that pony, one of the two we use is 26 years old, can pull that then your pony can easily pull a harrow.
Am looking for a harrow for my Odinn to pull, am quite jealous you have one, he needs to be doing something when not driving or being ridden!
Anyone have one going cheap???