Take a tripod. Your friend will be still except for when it really hurts
Use the 3200 and if you have lots of film, I would try a green for helping skin tones but I would also consider an orange (15 wratten #) and maybe even a red (25) though that will take a long exposure, but you might just get something cool.
The green will render more natural skin tones and the red will whiten the skin. If you need more light, take some with you. A bright 100 watt light with a piece of silk, rice paper, or translucent cloth of some sort to diffuse the light will help you and the tattoo artist.
Make sure you show us the pics!