Don't be skimpy. You want your paintings to last. When you frame and store your paintings, make sure that the other materials that come in contact with them are also archival. As it dries, it shrinks and pulls very tight and flat, and remains that way, even when re-wet. When I'm through with the painting, I remove the staples.
Watercolor paper comes in blocks of various sizes, or in sheets .
Cylinder mould made papers will always have two deckle edges. Hand-made papers will have deckle edges on all four sides. You can cut or tear these full sheets into smaller size sheets for smaller paintings. Paper also comes in different weights , from 90 lb. This paper is too lightweight to do any scrubbing or surface manipulation without risking damage to the paper surface.