Please be very careful not to leave any loose ropes near any horse or pony.
I would urge you to be cautious in putting this pony out on lush grass. Small ponies like this are very prone to laminitis (fever in the feet) if they are let out on grass and allowed to gain a lot of weight - and laminitis can cripple or kill them, cause chronic pain...or just make it so no one decent wants them.
If I was in your situation, I'd have him gelded and give him to a trainer that taught combined driving and the kind of pleasure driving that is similar to combined driving - in other words, no fixed rein holding the horse's head up.
I don't think he's a good candidate for any other type of driving - fine harness or the like.
In a month or two of work with a good driving trainer, he'd be a very good driving pony, and that would guarantee some more stability in his life. He'd be wanted and valued.
Combined/pleasure driving is really growing right now. There's a huge interested in driving for fun and enjoyment and going on driving club outings.
If he is 12 hands, his weight limit for a rider will be about 75-80 lbs. He could pull more than that in a cart, though.
Since he's only 12 hands and very well proportioned, that pretty much disqualifies a lot of animals as LIKELY parents.
When you cross breed horses you can get all sorts of odd results, but I'm going to focus on what's likely.
I would not guess this horse to have much or even any Halflinger blood. For one thing, he's rather small to have had even one Halflinger parent.
He is not the blond Halflinger color. Very few Halflingers are any other color than the blond. Despite having many around here, I haven't seen one that is not the blond color. It can be a little lighter, or a little darker, but the 'Halflinger Blond' does not have any of the dark silver effect on the mane and tail, nor the chocolatey color in the body.
Instead, his color is actually a chocolate sort of color, with a darker silver mane.
The color is most likely what is called 'Silver Dapple', not that it is silver or grey at all, but that it tends to put some silver into the mane and tail. It's essentially a chocolately or brownish, sepia color, with a lighter mane and tail. It is not yellowish-red like a chestnut or reddish-brown like a bay, it's a very different chocolately color.
Sometimes, if the coat is in very good condition, especially in summer, the brown coat will have light and dark areas, called 'dapples', but even so, all of the body color is still tthat same basic chocolate color. Dappled areas (light and dark areas) on the body can also be absent from the 'Silver Dapple' color, but the body still is that peculiar chocolate color.
Without papers, you'll never know for sure. Any guess is just a guess. I'm just going to say what's likely.
Among pony breeds, the most likely contributor of this color is actually the Shetland Pony breed.
There are two types of Shetland Ponies - a very small, thickset, short legged type, and a much more modern, slimmer, longer legged type.
The Silver dapple color does occur in Icelandics, but there simply aren't a lot of Icelandics in the USA - making that less likely.
My guess would be that he is a Shetland cross. Second guess, an Icelandic cross.
Too, sometimes ponies this small have one 'Mini' parent and one pony breed parent.
The silver dapple color also pops up in grade ponies that have a lot of different ancestors - the silver dapple gene does occur in other breeds, but the most often noted is in the Shetland and Icelandic.