1)60i and 30P are not the same. One is interlaced (60i) and one is progressive (30P)
2) The best settings for a doc depend completely on the aesthetic you are going for, and what you are shooting.
3) See number 2
You might want to check out the Documentary forum as well as the lighting and cinematography forums. Without knowing more specifics on what you are doing your questions are tough to answer.