I recommend starting with a treatment or two and seeing how things progress. Also during that time speak to your tattoo artist as to how much and what specifically needs to be lightened to achieve your goal. Normally tattoo treatments are 6-8 weeks apart and can take 4-10 treatments...
If the laser doesn't hit the ink in the tattoo, it will be safe. If the tattoos have any overlap or are up against one another, then you can have some collateral since the laser will likely hit the adjacent tattoo. These are easy to correct by going to your tattoo artist for...
All tattoos are different and so are the lasers used to remove them. Black ink is best removed with a 1064 nm laser. The Picosure works best for greens/blues/reds, not black. I recommend a pico laser if there is one available near you. Cutera Enlighten, Piqo4, Picoway are all good choices. If...