I don’t think everything needs to be a shared cinematic universe like Marvel. But if that’s what you want to do, put in the actual ground work. You can’t just do “Iron Man” and then have your second movie be “Captain America: Civil War”. Build up to it.

Even if you are coming up with entirely original characters for the shared cinematic universe you want to create. It’s much better to build up to it, so your audience cares about the characters and stakes of the stories.

Also adapting existing/known characters to a shared cinematic universe, you still need to do the work and lay down ground work. You want your audiences, not just people who are familiar with the source material, to care about these characters you are creating.