I would start with a forecart as my first piece of equipment. It usually consists of an axle with auto tire wheels, a long pole out the front. Has a seat for the driver. This will turn the pair of horses into a “tractor” that you can ateach implement to. Do you have any Amish communities near you? They can be a source of equipment, harness, trained horses.
Many working drafts are sold with their collar, because finding and fitting a collar can be time consuming. In choosing a pair of horses, you can go with smaller, but muscular animals, cross bred animals. The big drafts (show hitches, Budweiser Clydes use tall, leggy horses) can be expensive to maintain. They need grain, as well as hay, which can get expensive. The Suffolk mentioned before are getting a bit more common, along with their crossbreed offspring. They are not flashy, clean legged, and very economical to feed. Part of their appeal to the Amish is that they look good on pasture, minimal grain and still can do a good days work! They do have beautiful eyes. The ones I have met were pretty docile, liked people. Of course other breeds can work too, but seem to run to bigger animals.
My Grampa farmed with horses a lot of years ago. All of his working horses were smaller, 15-16H or less. He said it cost too much to use the bigger animals, in feed to work returned. Big horses did not stay plump on pasture and a handful of oats. They were harder to harness with heads way up there, higher backs to lift harness up onto for work on a daily basis . Shoes cost more, when they needed to be shod. He usually kept them barefooted in work and they could still pull well. He only got beat at the horse pulls by shod horses, usually placing 2nd or 3rd, for good prize money. His horses were mannerly at the pulls, he put the evener on the machine himself, no danger of them taking off like the other pairs! Mixed breeding, probably some old QH and draft. They did seem to all be the same lines “out of The West by Truck or Train.” Ha ha
Not sure if you can get away to attend training to learn draft animal training. Tillers International near Kalamazoo, Michigan has such classes. Their website should show the schedule of classes. Kayo Fraser of the Fraser School of Driving in Montana gets high recommendations from driving acquaintances. You could call them to see what is offered.
There are several Auctions selling draft horses and farming equipment in the midwest, Indiana has Topeka and Shipshewana, while Ohio has the Mt Hope auctions. Waverly Horse Sale is in Waverly Iowa. All the sales are coming up soon, March, so check for dates to attend.