Do you like it's a good or bad idea to start the story off from the not-quite-main-character's prospective to create a bit of mystery?:
I think it's fine to have a story that switches perspectives. However, you have to make sure it's done with purpose. Readers are going to be wondering why the perspectives were changed, and if the character whose perspective was first shown isn't a main focus of the plot or conflict, or if their actions in the opening don't tie in to anything important, it won't make sense and they may be confused. Mystery is always great, just make sure it's played off well.
I think it's fine to have a story that switches perspectives. However, you have to make sure it's done with purpose. Readers are going to be wondering why the perspectives were changed, and if the character whose perspective was first shown isn't a main focus of the plot or conflict, or if their actions in the opening don't tie in to anything important, it won't make sense and they may be confused. Mystery is always great, just make sure it's played off well.