My understanding is that the rationale behind the housing-first movement is that all the other interventions are much more likely to succeed for someone who has

My understanding is that the rationale behind the housing-first movement is that all the other interventions are much more likely to succeed for someone who has stable housing. There are a few reasons for this. One is simply that it's easier for social workers to follow up on someone when they know where to find them. Another is that in order to become eligible for most types of assistance, one needs to list a home address on the applications. This includes job interventions, adult education, food stamps, and the medical benefits that support addiction and mental health interventions. Perhaps the most important is that stable housing removes one of the greatest stressors from a formerly homeless person's life. If you're constantly worrying about where you're going to lay your head at night and whether you'll be safe there, that's a) a constant source of anxiety that's capable of exacerbating mental health conditions or driving someone to drugs; and b) doesn't leave the mind free to worry about longer term fixes for the situation. Moreover, the prevalence of drugs on the street and the lack of anything else to do with one's time, other than worry, also drives people to use them and makes breaking existing addictions harder. Even a television would be at least a distraction. Organizations that not only perform interventions but also study their efficacy have found that compliance rates for things like taking daily or weekly medications are much higher if people are first put into stable housing. I applaud your desire to address the problems of homelessness in ways that existing players are failing to. You may first want to research what has already been learned in this space.