RE: knuckle cracking and arthritis
As a guitar player, I can tell you that finger cracking does have some effect on your joints. I used to be a finger cracker, and after I learned guitar and started playing all the time in a few bands my fingers would hurt at the joints. Somewhere along the lines common sense told me to quit cracking my knuckles, and the problem with my fingers hurting gradually went away. This being while my guitar playing got more complex, and I started playing in a band that was in high demand.