I don't know about other people who do knife and blood play, but I have found as long as you and your partner know what you are doing there is little risk in it. Most of the cuts have been small and in areas that aren't super easy to do somethign wrong. But when we play it is more about the sight and taste of blood than the amount.I guess part of it has to mortality because my enjoyment of it stemmed out of an interest in vampires, but I like the feeling of sharp things on my skin.
We also use several knives, there ae ones with cutting edges adn ones that are blunt that my Master uses in more delicate areas. If you don't know which one is in use then it ups thesensation. Even a dull blade can feel sharp in certain areas. I have heard if you put it int eh freezer it feels sharper too, but haven't tried that yet.
I have no expirience or desire to try breath control, so I can't say anything abotu that.