A nice set of pics Mikkel, and yes, rug is the correct term for the horse rug.
Regarding your horse size, as you say, it can easily pass as a yearling. Unless you are trying to pass it off as a full grown hunter I don't see the problem! You could even re-profile the head, paint it dappled grey and it'd pass as the Arab mare I once owned that was only 14hh fully grown and definitely not a pony.