I am going to use the ball pan to do the teapot. Do I put a filling between the two halves? Also I may set the teapot on top of another cake, will this work if I dowell it real well? I am going to use lollipop sticks.

I would say yes it would work to fill it if you're going to dowel it and yes definitely put some type of dowel if you're going to sit it on another cake, might not be a bad idea to stick a small cardboard circle under the teapot too to displace some of the weight and it would make it easier for serving purposes too.