No, I checked this out before starting this thread. Since the bear form is a polymorph effect, you cannot rage into bear and then turn into a bear again. (Or vice-versa.)
A new rule occurs: Please ignore Errata, since I don't use it.
No. You need to be able to pull it off solo.
If you can pull it off with these books, sure, I'd like to see it. But actually using it in-game would just get me smacked upside with the DMG.
What's the Warshaper 1 for? The +4 to STR and CON doesn't kick in 'til Warshaper 2.