Karameikan Adventure Flow Chart
by DM NedleedsGlad to hear you got started. I too started a campaign with 4 new players this past Christmas about 1,000 AC. I set them about 10 years after the events that would have happened in Red Box. In this case a failed quest to bring Bargle to justice (based on the Tales of Mystara podcast actually).
I start the game with 1 of each class (F, C, MU, T, D, H, E) "in media res" as all being a part of a caravan heading North to Threshold. Several were passengers others were guards or roadwardens (the dwarf was actually at a logging camp). As they stop to refill their water at a friendly logging camp just South of Verge I initiated an ambush by Hobgoblins. Expecting some of the PCs to die in the encounter, the surviving PCs then move on. The Hobgoblins have a map, with dates marking various caravans (past and future) and thus begins the quest to understand who is coordinating this assault on commerce.
Anyway, from there I have a light set of plot points that can flow into the published modules and Castle Mistamere. In my campaign I have The Master pulling the strings by financing various hobgoblin chiefs to war with each other in order to disrupt the Duchies prosperity and keep them uninvolved in his crusade against Darokin. He has set 3 chiefs at war with each other using various agents in Threshold, Castellan Keep, The Hill (Guido's Fort) and even Specularum.
I'll get the framework published one of these days but it has a flowchart, and hooks for whatever direction the PCs decide to go. My recommendation is use the Duchy as a sandbox not a railroad. There is so much material that no matter where the story goes you can plug something published into it.