That's kind of how I go. Usually when I envision the story and start working on the chapter, one point jumps out as the scene that will be a chapter-ender, and I just go with it. That meant that my previous project (pretty much finished, now!) was only 14 chapters, despite being over 100,000 words long. I originally thought there would be twelve, but that just goes to show you what I know. Some chapters ended up being over 10,000 words.

Also: "Parameters are good. Boundaries are very bad."

I couldn't agree more.

I really have no idea how many chapters this new project will be. I'll figure it out when I start writing.

That sounds quite complicated... trying to get both sides, independently-created, to mesh well together... >_<