How common is travel?

On one hand, it seems like most people shouldn’t venture far beyond their closest urban settlement. If the typical pre-industrial person doesn’t travel more than five miles in their lifetime - and I don’t recall offhand where that tidbit comes from - most people have never been out of their hex, but they’ll know that hex pretty well. The only people likely to travel more extensively would be people in merchant caravans, someone’s army/warband, courier services, and a few other odd sorts (like adventurers).
On the other hand, the effects of domain morale on population suggest something more fluid than that.

I’m not actually sure where that oft-cited tidbit that the typical pre-industrial person didn’t travel more than 5 miles in their lifetime comes from.
I think it was certainly true during the middle ages, because most of the population were serfs, and serfs were legally tied to the land. But, for example, during the era of Classic Greece, any given city-state was at war 1 year out of 3, and every able-bodied male citizen was recruited into the army. They certainly marched more than 5 miles from their home on a regular basis. For that matter, the area of the city-state itself was larger than 5 miles in radius, and male citizens were expected to travel from their estates (farms) to the city regularly.
As far as domain morale, even the most isolated populations were visited by merchants and bards who carried stories and information. That can have a big influence. Consider the immigration to the United States in the 17th - 19th centuries - it’s a certainty that all those who immigrated there had never been there or knew anyone from there, they did it based on the rumored promises of a golden land.
That said you could certainly tone down those effects if you wanted to create a more isolated, immobile population. Strahd’s Barovia, for instance, clearly has low population mobility…