I don't think it's obsessive to shuffle, it's a relaxing activity, and I am kinda of an OCD person to begin with, so I could be doing something alot worse than shuffling lol, but to each his own.
I only shuffle when I'm listening to a querent state their question or problem. Otherwise, no, I don't shuffle my decks as a pastime. I never played card games when I was younger and it took me years to master shuffling when performing professional readings.
Constantly. Especially when I am relaxed. I scuffed up one of my decks already from constant shuffling, so I try to do it with the decks that have thicker coating.