I now have a working wandering merchant who, along with a guard and pack horse, traverses winding forest trails through 3 large maps, setting up shop for a spell in each. Rather like the merchants in Fallout 3, which was what I was aiming for.
I used Axe Murderers' Killer Walkway system to make the merchant wait at each of the 3 market locations for a spell, and L8s' suggestion solved the Merchant inventory problem. Still a few kinks (merchant won't stop if you meet him between markets, so you need to shop fast) but as I get more familiar with the KWW system I reckon I'll suss it out.
Thanks for the feedback!