Do edits on songs in one "project" affect the other projects?
Add a song from your project to a bandmates and they wish to edit at will, will it alter the original version or alter a "copy" saved in their profile?
Yes, edits to one song will affect that song in every project.
If you want to have a different version of a song in a different project, you can copy the song and then assign each copy to a different project.
Alternatively, if you want to have different data for each band member, you can turn on some of the settings in Settings > Account Sync > Personal Sync and then you will see a Shared and Personal version of each field. That's probably what you want instead of creating separate projects and separate copies of songs.
In general, your bandmates should not be using different projects than you. Projects are meant for if you play in several bands, then you would use one project for each band.
My intention is to have all band members share the same project and be able to edit their copy of "charts" to taste without changing my copy as the master keeper.
Please describe the best way to do this, thanks!
If you are using the built-in lyrics and chords fields, then any user that wants to have his or her own version of the lyrics or chords can turn on Settings > Account Sync > Personal Sync > Lyrics or Chords.
If you are using attached documents, you can select a subset of users to see each document.
More info is on this page; you can search for "personal sync":
http://www.bandhelper.com/tutorials/synchronizing_devices.html