For this story, I've decided on a fantasy/journey/quest vibe, as if it is a story being read to the audience by a wise old wizard. I've been reaching to The Hobbit for inspiration on the language to use, and old (classic!) Dungeons & Dragons adventure modules inspiration on the structure of the quest the characters undertake.
I've sought to craft an unsympathetic main character. While certainly villainous, he is not exactly the antagonist. He joins the sympathetic heroes on their quest in hopes to gain immense wealth, preferably at their expense. He is a liar that can not tell the truth, always believing he can talk his way out of a mess. This adventure is not his usual scam, and he'll find that not every situation can be resolved with a silver tongue.
The other characters - heroic adventurers - are lifted from other stories of mine, at least two of which were D&D characters I've played as in the past. They will trust the villain, naively so, because they are generally young and lacking much experience with unsavory types. I envision this tale as just a side story in their epic -- they are stars of many other stories, but this isn't their primary adventure. They would be recurring characters as a team as well as having their own solo stories.
To help visualize the adventure, I've been creating outlines and drawing maps. Hopefully this will help keep the pace quick and the adventure full of interesting dangers for the heroes to overcome.