How to plan a long-term creative project for serial publication:
1. Make a firm decision about how big a single update is going to be, and estimate your sustainable update frequency based on that. This estimate should be based solely on your own demonstrated performance; you may anticipate that future productivity will exceed past productivity, but never make long-range plans on the assumption that future productivity will exceed past productivity. That is called the Planning Fallacy, and it will eat you alive.
2. Estimate how often you’re likely to miss updates. As a rough guideline, if you’re physically and mentally healthy and have no major commitments that would interfere with your ability to work on the project, figure that you’ll miss about 10% of your updates for various reasons. If you have health issues or frequent Real Life commitments, make it 20%. If 20% sounds low to you, you weren’t being honest with yourself about your sustainable update frequency; return to step 1 and re-assess.
3. Figure that you’ve got about two years before you lose interest in the project, gain some new commitment that will preclude continuing to work on it, or your art style evolves enough to make creative continuity impractical. If there’s some upcoming major life change that you’re able to anticipate – like, say, graduating from school – use either two years or that event as your soft deadline, whichever is less.
4. Use the figures from steps 1-3 to estimate how many updates you’re likely to be able to squeeze into this project, and write your outline/script based on that. You don’t need to wrap up every tiny little loose thread by that point, but ideally it needs to reach a point where you could stop and be satisfied with whatever conclusion has been reached. If you get there and you’re still enthusiastic about continuing, fantastic – return to step 1 and re-assess.
So, as a simple example: if you’re planning a webcomic, you figure you can reasonably manage about 1 page a week, and you’ve got a lot going on that’s likely to get in your way, that’s (2 years * 52 weeks/year * 1 update/week * 80% success rate on updates) = around 83 pages to work with, or about the length of a four-issue miniseries. What kind of story can you tell in 80-odd pages?
(Hint: it’s not a story that involves fifty-page combat scenes!)