I can't help you with the oceans, because only you know what your story needs, and it's possible that it will turn out to need something else entirely once you are in the middle of writing it. It may help to draw your own map, just to keep track of where things are when you are describing them, so you don't have your characters make a four-month journey in two days. If the story absolutely requires that the journey be made in two days, either think of a way (magic, whatever) or draw a new map that allows that to work and revise the rest of the story to allow that.
All history is incomplete because no one book can encompass it all, even for a small area. Thus all history involves much the same sort of choices that fiction does. Satire and Comedy are ways of writing, not genres. For instance: there are satirical cowboy stories and comic cowboy novels that are not satirical. There are satirical romance novels and comic romance novels, and romance novels that are satirical comedy, though that is much harder to do successfully. (Some of Georgette Heyer's books are satirical comic romance novels, but most of them are comedy of manners.)
One of the techniques pTerry used was to set up a situation in which one thing was different, figure out the logical consequences, and then write the story absolutely straight, with the characters having normal responses to the world they live in. The satire happens in the reader's mind, not necessarily in the written page. For example, in science fiction the characters don't go around saying "Gosh, look at this wonderful futuristic thing I'm doing." They just do it, the way people who grew up before computers were available just use their handheld phone to send email and forward pictures to their grandchildren. Similarly, in a magical universe, no adult is likely to be astounded at the simple existence of magic, because it's a fact of life for them, like weather or solid objects (assuming they're not gaseous bubble creatures living in the gaseous envelope of Jupiter). As readers of such a story, we might be pleasantly surprised by the style of magic in such a universe, and we might perceive the gaseous creatures as resembling modern politicians in their insubstantial world of politics, but the story shouldn't tell us that in so many words. It should give small clues so that we can make the connections ourselves.