Well, theoretically, Seasonal Spuffy entries should be new stories. But the way you started "Thought You Should Know" you could easily circumvent the rule by tagging it as a one-shot prologue for a bigger canvas. The story works well as a standalone, and you could develop the "main" story from, say, Buffy's POV. It depends on what you plan to do.

Anyway, I'm running to your LJ to read the next installment! :)