You can make all your discs waterproof with a clear coat of Acrylic spray which you can buy in all crafts stores for around $5. I haven't found the surface of the verbatim's to be sticky, however the spray will solve that problem as well.

Why would you want to "stack them with eachother"? You should keep them in a case for the best protection. However, after they dry, I'm sure you could stack them together if that's what you want.

Sorry if I am misunderstanding what you mean by "stacking them with eachother".