You can peel the bark now relativly easily. You may also wait untill later and it will tend to flake off rather than peel, but that is still okay. I'm told you could soak it in a warm shower for a half hour or so to help in removal, but I haven't tried that. Lots of things will work to seal the ends. Elmer's School Glue, Titebond...pretty much anything to form a barrier to prevent water quickly escaping. I don't think you'll have too much trouble with checking in elm anyway, but sealing the ends won't hurt and may help. Be sure to leave the stave you plan to work on a few inches longer than what you want the finished bow to be too. If it does check any, you can remove the damaged bit later without hurting your bow, amongst other benifits.
Enjoy!