The first thing I'd like to point out is that most of this is involved in creating pain on another being besides yourself on the physical body.
The first thing I've noticed from others and myself: The amount of energy you'll need for the task is massive, and if you try without having a shit-tonne of your own inner energy, not energy that is from ambient or elsewhere, you'll have a hard time doing this.
The pain I'm able to cause today was a lot better than yesterday, I've made stomach cramps and headaches. Visualization doesn't seem to work as well as it would with other techniques. Massive amounts of energy and focus are required or you'll simply phase out of the physical plane.
In total, that's about all I've noticed so far.