Serial fiction as episodes
One of my models for this serial project is TV shows, as I've mentioned. I don't want to be completely tied to that idea, but so far it's been useful as a way to frame the project (and a way to give my mind a pattern to aim for). So one of the things I did as I was debating how to proceed was to look not just at how individual episodes flow but at how TV seasons are structured.
I don't watch a ton of TV, so some of this is perhaps more obvious to people who do, but I found that in the US a typical season, at least on network TV, is 22 episodes long. They'll contract for the first 13 including the pilot and then do an additional 9 if the opening run is successful. Cable dramas recently have been using a straight 13-episode season recently, though. And even that is simplified, since recent shows have ranged from 6 to 26 (and a few decades ago the typical season was 29-39 episodes).
22 episodes seemed somewhat of a stretch for me to plan out right now. So I decided to plan out the first 13 with a definite arc and a definite season-ending finale, but that leaves things open as to the overall arc that I have in mind for some of the characters. Who knows, maybe as I get going through the first few episodes, I'll see the potential expand and add in another 9 episodes...but I'd have to add them in to the middle somewhere rather than tacking them on at the end. I'm thinking it more likely that I'll just save up any other ideas for later seasons.
Really it's probably silly to worry a lot about that kind of long-range planning as I'm still working slowly through the first episode (the pilot, I guess). I fully expect the pace of writing to pick up, though, both as I get a better hang of the tone and such and the structure of the episodes and as I get the hang of finding writing time with 2 kids. I was doing 3-4 chapters a month with my most recent novel, and I expect I could set a similar pace with the episodes eventually. Plus...I find it fun (and useful) to challenge myself to think of writing in a completely different vein like this.