You raise a lot of interesting points. I've always been a little fascinated with the Happy Mask Salesman and those images and symbolism inside the moon. In fact, last year I created my very
first thread on ZU about the same subject. What makes him particularly interesting is how enigmatic his character is. He's one of the central pieces of the game
Majora's Mask, but we know very little about him. He's just presented as someone who wants his mask back.
I've always wondered whether or not the Salesman is the last descendant of the mysterious tribe that forged Majora's Mask. It would certainly explain how he got the mask in the first place, and it might explain the appearance of the children in Termina's moon. Furthermore, it would make sense that the Salesman would specialize in masks if such a powerful mask was handed down to him over the years. If you look at it the right way, that solution would answer a lot of questions about him.
The first time I played through
Majora's Mask, I didn't completely trust the Happy Mask Salesman. His mannerisms, the way he spoke... He
really wanted that mask back. Maybe he was simply holding onto the mask so it wouldn't be abused, but the whole thing's a little fishy. It's entirely possible that he wanted to
use the mask. I dunno. Power tends to corrupt, so it's a possibility.
That's one of the best things about the Happy Mask Salesman. There's so little we know about him, that it's fun to speculate and theorize about him.