I don't think it's the edges at issue
I have no experience with pre-finished plywood. I do know that you can't just finish one side and have it not warp.
If you want to paint over an existing finish, the paint must be compatible.
Check the specs to find out. Water base is probably the best and the most safe.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
Last edited by woodnthings; 01-06-2014 at 12:48 PM.