I'm hyper-orgasmic, so the most times I've orgasmed in a single session was 53 times. That was with my ex-husband, who wanted to figure out the upper limits of my gift, and it took about two hours to orgasm that many times. I probably could have had more, but I lost consciousness for a few moments and told him we needed to stop before I really hurt myself. He used to say if we could just bottle my talent, we'd be the richest people in the history of the world.
So... as a hyper-orgasmic person, my preference is to keep it under 20 in an hour, because otherwise the stimulation gets to be too overwhelming and they stop being as satisfying. By myself, I usually stop around 10. And just about any kind of stimulation works - if I'm turned on enough, having my partner talking to me in a low voice can trigger an orgasm.