Here are the things I'm trying to figure out:
-Roughly how far, on average, can they travel per day? (They're not sightseeing, but they're in no great hurry either.)
-How would the driver take care of the horses, since they're not changing teams as on a stagecoach route? (How often do they have to stop and rest, etc?)
-Would I assume a coach drawn by two horses, or more?
Search terms I've used in many combinations: road travel, speed, time, private coach, road transport, types of coach, carriage, grand tour, 18th century, 19th century, 1700s, 1800s, France, Italy, history of road travel, history of road transport... I've also tried -stage and -England, since a lot of what I've turned up deals with the advent of stagecoaches in England.