Hey Manuel. I just saw this thread. I don't know if you're still looking for advice; you're on your tenth episode, so you've probably settled into your own method for organizing your content. But it occurred to me that what you're doing is sort of similar to writing multi-chapter fanfiction -- with the notable difference that what you're doing is professional and much more original.
Still, it's similar in that you're writing it "chapter by chapter" the way ongoing fanfic is written, there's an audience waiting for each segment, each piece has to be entertaining in its own right, and you can't go back and change the things that have already been printed.
There are two things that I worry about when writing a new chapter of my story: 1) that the chapter I'm posting isn't entertaining, and 2) that I'm introducing something inconsistent with what I've already published or missing a chance to post something that should be included.
Not every chapter can be an earth-shattering event. In every chapter, I try to make sure the chapter begs a new story question and either answers one or at least brings the story to a new level of questioning. I try to make sure my chapter moves the story along--the characters complete a task, finish an important conversation, or get ready to move to a new location. I try to introduce something new about a character, the world, or the storyline.
As far as keeping things consistent, I just make careful notes (the way you are with your spreadsheet). I like to write my chapters all in the same Word document. I have a general idea of the overall plot, so I have placeholders for chapters where I've made notes that spread the story out over all the chapters. I also make notes about things I need characters to do in between--like, if I know a character has to open a door in Chapter 12, I make sure I leave a note for myself in chapter 15 for him to get the key somehow. If I know something has to happen, like Character A needs to mention a fact so Character B knows about it in Chapter 14, then I'll add it to a collection of notes that I carry from chapter to chapter as I write. If I can work one or more of those notes into the chapter I'm writing, then I do so and then remove it from my list. If this chapter isn't a good place, I cut and paste my notes into the next blank chapter. That helps me remember what things I needed to do.
I also have an important object that changes hands frequently, so I make a note at the beginning of my list about who currently has it.
All in all, having placeholders for my chapters lets me go in when I get an idea and makes notes about it in one chapter or another. Eventually those chapters with notes start to form a nicely detailed outline.
Something else I struggle with in these one-chapter-at-a-time stories is that I do get to see reader feedback in between. Some people are really happy with what I've been doing, and others not so much. Some of the more vocal readers tempt me to change direction, but I've realized that when I change direction to make one reader happy (and then change direction, again, to make another reader happy), it leads to inconsistency in the story and in the characterizations. There are certain things you can change to satisfy readers that don't really affect the overall integrity, but you have to know what will and won't hurt your story and stick to your guns if you're routinely reading feedback on the forums.
I also agree with Maryn's advice to write ahead. In my story, I'm currently behind because I don't have the next three chapters written... however, I do have several chapters after that already mostly written, so when I go to post those, I'll have some nice breathing room. It's hard to write ahead (I'm such a procrastinator), but you just have to make yourself do it and remind yourself that you're going to much happier in the long run if you're not stressing out about deadlines.
Hope the 10th installment is going well!