You strike me as someone that would benefit from structure.
Take one of those What If ideas and apply it to the heroes journey outline.
If you want to plan everything out in advance than an outline is the way to do it!
Here's an example I wrote once for a soul mate of yours that is no longer with us
1 - The Ordinary World
A man is paralyzed by the most nuanced of technical choices. He wants to make a film but he doesn't understand how to fix problems by himself so he stays glued to his computer screen, posting in an indie film forum.
2 - Call to Adventure
After years and years of making no progress the man is starting to feel his youth slipping away. Somehow with all of his questions and all of these answers he still hasn't made anything. Someone suggested film school so maybe that's the answer. Film school works for certain people, someone told him that once online.
3 - Refusal of the Call
He's given a homework assignment. But instead of trying to learn and grow as a person he goes back to the forum and makes more threads. He's caught up in the same cycle over and over again.
4 - Meeting of the Mentor
One of the moderators says enough is enough and bans him from the forum. The moderator says it's tough love and the best thing for him. Under his breath the man mutters back to himself "thanks, but..."
5 - Crossing the Threshold
He snaps and yells. He unplugs the internet. With a giant sweeping motion he knocks everything off his desk.
He pulls out a piece of paper and a pencil and does his own homework.
6- Tests, Allies, Enemies
Nobody wants to work with him. He doesn't give up, he keeps trying to get people to work with him.
He goes to the professor and says he can't make the film alone, the professor sets him up with the resources.
7 - Approach to the inmost cave
He stands on his set. He looks around imagining. He holds out his hands framing a picture.
He alters some decorations and puts up a different photo in the background.
8 - Ordeal
Finally he films!!
9 - Reward
The first edit is complete. He stands on his desk and proclaims loudly Behold what I have wrought!!
10 - The Road Back
He likes an edit better without all 12 steps of the heroes journey. Why is this story still going on, the interesting stuff is over isn't it? Maybe he should make the best product instead and get a lower grade because he wants people to work with him in the future and he won't always have a professor to give him the resources.
He decides to drop the last couple steps of the heroes journey and end at step #9
11 - Resurrection
People like his film and tell him he did a great job. His professor says that he's disappointed in him for not rising to the challenge. He says that films are all about compromise and only the people who are talented enough to work within the constraints they're given will make it in this industry.
He snaps his DVD in half and throws it in the trash. He goes back to his editor.
12 - Return with Elixir
He creates a new indie forum account at the library and apologies to everyone for all his endless complaints and questions. He says that nobody is perfect and certainly not him, he understands now that film is about how much you can do in a given time. It's not about taking years to make decisions it's about taking action.
He logs offline and doesn't wait around to read what anyone says about the film.
He pulls out a blank piece of paper and a pencil.
He writes
EXT. JUNGLE NIGHT - DARK AND STORMY