But what happens when you get more reviews or when you post more installments and then realize you need to add more to your index post?
For example, let's say you can fit at most ten chapters to an index post. (Not saying you literally can. It's a figure.) At this hypothetical moment, you've got five chapters done. So, you decide to have ten chapters in total at that point. As you post your chapters, you do it in your index post and in the rest of the thread. You also get more reviews. However, when you've reached chapter ten, you realize you haven't gotten done everything you wanted to get done in your story. You then have two choices: either to write a crappy, rushed ending so you don't have to create another index post or create an index post right then and there, two or more pages after the first post of your thread.
In other words, either way you're restricted. In order to prevent the above from happening, you need to know everything that's going to happen before you write your story, and you can't change things except to make things shorter unless you overshoot the character limit and are forced to make a new index post posts away from the first one. So, you end up with a rushed plot because you're cramming a lot into a small space thanks to the knowledge that you have a character limit. Yet, if you don't anticipate it by restricting yourself early, you end up with a disorganized thread.
Long story short, seriously. I really suggest you don't use this format. It's not going to be innovative. It's just going to end up being a hassle for you and the people you're trying to benefit.