As for the first item, v2.2 will have two features that will help you out here:
1. The ability to work with centimeters or inches, as well as pixels. So you can draw a 4in x 6in rectangle instead of 384 x 576 pixels or something.
2. The ability to transform selections, and selected pixels. "Transform" refers to the ability to move ("translate"), scale (stretch/resize), and rotate.
As for moving shapes, that is not something we will be able to undertake for v2.2. Maybe later, however, as Paint.NET's code architecture is quite versatile.