hiya I have had a look for you.
Your breeaching needs to be lower on the rear buckle.
Your breeaching is your brake.
Your neck strap on your collar has no rein ds and lacking in padding I think that would rub on your ponys neck when he sweats.
Your crupper is lose and needs to be titened up rule of thumb don't trap no tail hairs follow a thinger through to make sure there are none traped or the pony could buck.
The tugs seems like there is no back band as no independent movement and the driveing saddle pad may move and rub the withers and the girth will rub as well.
The breast collar hight looks ok have a check with your hand as you don't want to pipe your pony (restrict the windpipe).
If you use the over check have it lose the buckles to the bit seem bulkey you can use it as a dasy rein as one member stated I think replace it with a nose band.
I hope this has given you some idears and I hope I have not been critical of your harness I have your self and your ponys best intrests at hart and would like you both to have great driveing times togeather.
Many thanks michael.