Subculture- Homelessness

I intend on reading various books to help me gain a better understanding of the subculture before i jump in and start conducting interviews for my research.  My sources for research will be made up of a lot of interviews hopefully. Visiting shelters may help me find people that will be willing to participate in my understanding of there cultures.   Also I saw a video in my Sociology class last semester that talked about a different kind of homeless person that most people are not aware of, which is the "hidden homeless."  Videos may also provide good information.  

I can't really imagine what types of behaviors, patterns, rituals, and rules. etc to run into, but I think that I may run into people with maybe some sort of mental disorder.  Only from what I have gathered from previous experiences.