Interesting…
Ok I’m hopping in this thread and while I’m a huge music fan I’m not one to know all this history and details. I’ve always wondered about the bridge thing though - thanks for clearing that one up! 
Didn’t the band, sans Plant, also all play together on some Donovan tracks prior to Zeppelin? I though I remembered reading this somewhere.
Which is why Live at the Apollo may be one of the best recordings ever made.
Page, Bonham, and JPJ all played on Donovan’s song Hurdy Gurdy Man. Not sure if there were others.
Yes. The “Hurdy Gurdy Man” track, for example, is basically the three members of Led Zeppelin with Donovan on vocals rather than Plant.