@EightBitz: You seem to have a pretty good grasp of how WE intended Realm Works to be used. If the one-off adventure is part of the overall campaign, then it should probably be part of the larger realm. However, if it's just a one-off throwaway game, then it should probably be a completely separate realm.
Just because it's how we designed the product to be used does NOT make it the "right" way of using the product. The one advantage (and drawback) of a massive and flexible product like this is that you can leverage it in so many different ways. The real question is what works best for how you operate as a GM. To that end, I recommend the test realms approach that you've already begun and some experimentation with different approaches.
