Paper will hold up fine if it's a high pecentage of rag composition (cotton or linen) rather than wood pulp, and is properly sized. No glass is required in that case. I've seen oils on paper by Constable that are over 100 years old and in excellent shape. They were mounted to either wood panel or canvas.
Shellac flakes can be found in a "white" or "clear" variety, but is still a slight amber in color. Look for the de-waxed/wax-free type. Most pigment sellers carry it, or fine furniture/woodworking places. The flakes are diluted in denatured alchol. Please avoid the pre-mixed liquid in cans (Zinsser) as it has additives to extend its shelf life (mixed shellac will spoil like RSG) which you don't need.
Here's a good US supplier who also carries a nice selection of resins:
http://www.woodfinishingenterprises.com/varnish.html#