Is there a way to mass move items from your inventory to your shop that way you don't have to do it one item at a time? Also how do you get the backgrounds for your human avatar?

Yes, click the name of your shop you want to move the items to, at the top there'll be an option called QUICKSTOCK

Different items give you the backgrounds. If you want to see every item that gives you one, go to your wardrobe and look at all items on Subeta. Then click the layer that says backdrop.

I was thinking about mailing you then just didn't wanna bother you more.

lol, don't worry about it. :3 My inbox is always open.

I still can't find it even after playing around this long :(