My approach to outlining: For each scene, write the minimum that reminds me what I want to accomplish with the scene. For me, the minimum is something like:
- The POV character.
- What the POV character is trying to accomplish in this scene.
- The conflict (who or what stands in the way).
- The outcome of the conflict (yes, no, yes but..., no and furthermore...).
That's usually enough to get me writing the scene. If there are other things I want to make sure to include (a clue, a revelation, a relationship event, a description of something in the setting), I'll note those, too.
I stop with the bare minimum. That gives me the energy I need to get into the scene, and plenty of freedom and opportunity for discovery as I write.
Though I don't worry about length before I write, this can give a sense of the length of the story. My scenes tend to fall between 800 and 2000 words (2000 words is a long scene for me). I figure 1500 words on average. So if I have 10 scenes, that's about 15,000 words.
I can often get a feeling for whether a scene will be shorter or longer because of the nature of the conflict--how the POV character will try to accomplish the scene goal, and how the conflicting characters will interfere.
So if your bullet points represent scenes, and you know how long your scenes typically run, that can give you a ballpark estimate of the total length of the story. If your bullets represent something smaller (e.g. beats or interactions within a scene) or larger (e.g. chapters or sequences), you'll have to adjust, based on your experience of how big those chunks typically turn out for you.
You may need less information, or more information, or different information. My recommendation is to experiment, practice, vary your outlining from story to story or scene to scene to discover what helps you and what hinders you.
Try adding a few more details in your outline, and notice how that affects what you write, and your eagerness to write, and your satisfaction with what you write.
Try putting fewer details in your outline, and notice what happens.
Try outlining only a scene or two ahead of the scene you're currently writing. Try outlining many scenes ahead of your current scene. Try outlining only after you write the scene, to capture those things that you'll want quick access to when you write later scenes.
What other ways can you think of to vary the way you outline? Pick one or two variables and experiment with them. Keep experimenting until you discover what works for you.
And experiment now and again, because your needs will change over time.