] How did one man on one horse suddenly become a man, a horse, and his servant? Would not any servant also have to have a horse? Something about this scene eludes me.

As postulated below, Edward must have had a servant on horseback with him; riding, perhaps, some little distance behind him. But servant with horse there must have been, because at the beginning of Ch. 18, Edward walks into the village to see his horses. Plural. Had he been alone, surely he would have had only one horse. Perhaps his servant was the incredible Invisible Man. ;o)