It's fascinating to hear that, as I assumed when writers talked about having dialogues with their characters, it was metaphorical. I suspect it varies widely from person to person, and has to do with how your brain is wired. Another fan fic writer I talked to about this talked about having "cinematic" visions and building a story around them. I admit (with some embarrassment) to acting out some scenes, partly to provide a reality check so the dialogue doesn't sound too writerly and partly because that's how I told myself stories long before I wrote them down.

I suppose more elaborate plots have to be puzzled out in a more tedious way; I know JK Rowling kept masses of notebooks and mystery or thriller writers presumably have to map the whole thing out before they start to write.

I'm glad your story is no longer giving you fits and that you're enjoying it. I am truly looking forward to reading it.