They are big and need to be handled as such. You must demand more respect from them than you would a smaller horse. They are very calm and relaxed, but because of there size can unwittingly do major damage. If he is ridden in a halter, was probably broke/owned by Amish. They work horses in bridles but the kids ride them in halters because they aren't "working".
Other than ground issues and tack fit, they aren't much different than other breeds. You should mount from a block, although they are big, you can pull their shoulders/withers crooked from struggling to get on.
The dancing around may be from being in a hitch. For the most part once a "header" [someone holding them, stands @ head] is no longer in front of them, the reins/lines are picked up, and off they go.