Did I never reply to this? Maybe I did in Aim and don't remember. Maybe I didn't. Whatever. Here:
Yes to Teagan/Rona! Let's get a Scooby gang together for yarnsploration. THROW RONA AT MARCUS!
Holly/Marcus can totally have history. Though if you want that kind of thing... maybe he was too overconfident in the beginning and she get fed up and cold-shouldered him before he could truly hit it? Generally, he loses interest in anyone after the initial chase, so the chase would have to've been unsuccessful to get under his skin at all.
He'll treat absolutely nobody like a princess, so that will also work. XD