The "entire thing" takes place in five episodes, Mortal Folly, Mortal Recoil, The Lich, Finn the Human, and Jake the Dog. You don't need to know anything to watch any of the other ones. That's not to say there's no continuity between them, it just shouldn't be too difficult to catch on to what's going on. I feel like they follow that old Stan Lee line about how "any comic could always be a kid's first" (paraphrased and half remembered). Speaking of which, I gotta get some of those comics while the show's on hiatus...