Yes, yes I am aware that the 3 negs around the shutter would have to deal with inserting the film, but as for its effectiveness, do you think that is the best mechanism for what I'm trying to do? I think I found a really clever and simple shutter here that I could copy:
That means I have to design a way to advance the film but that's doable.

But do you not think these are the best ways to do this 3-shot deal? What would you do if you were in my shoes?