<One time his dad hit him so hard onstage,
he fell into the orchestra pit
and went head first into a tuba! >

I don't recall this anecdote, which is not to say it didn't happen. Buster had a handle sewn into his coat and was routinely hurled into the wings and the orchestra pit. Once Joe threw him at a heckler, telling him "tighten up your asshole, son" and broke the fellow's nose.

There is an incident when Joe was doing one of his trademark hitch kicks (he performs one in Our Hospitality) but because of his heavy drinking his timing was off and his knee caught Buster in the back of the head, his body went rigid and he collapsed and was unconscious for 18 hours.

Have you seen A Hard Act to Follow, the ITN doc produced by Kevin Brownlow and David Gill and narrated by the late Lindsey Anderson? I recommend it to fans of Keaton. They show footage in that from This is your life, in which Marie Dressler describes a typical Keaton routine. Buster is swinging a basketball on the end of a string that gets closer and closer to Joe who is standing with his back to Buster shaving himself with a straight razor. Buster sort of recreated it in Convict 13.

Neighbors, also features the type of Joe and Buster gags they were famous for in their Vaudeville days.

I stand corrected and thank you for your addition!
At least it sparked some dialog...
Anything else you've got?

It depends who you believe. You're right Houdini was the one in Buster's oft repeated story. Marion Meade casts doubt on the story in Cut to the Chase, pointing out that in 1904 in an interview with a theatrical trade paper, Joe claimed it was a fellow actor in the Mohawk Medicine Show, one George Pardey, who gave him his monicker after the famous tumble down the stairs. Depending on when the fall happened, Joe says 18 mos, Buster claimed 6 mos, they may not have even met Houdini at the time. By most accounts Houdini was hired by the medicine show at the end of 1897 when Buster was past his second birthday.