Once this is finished, is it like a box that needs to be solved to open, or is it just a box?

When you start construction you set your own combination. You need it to open the box. And there's a handy place to wright the combo on the box!

I am rubbing the wax onto the wheels, lightly. Is this enough?

Pro tip: Get some food-grade wax. A small amount will seal and preserve your project, and adding more to critical areas provides lubrication for moving parts without making a greasy mess.

How do i get replacement parts?

You can directly contact the seller to get the replacement part for free.