I'm so glad to hear your son is doing well and is safe. You must sleep so much better at night.
If you can give any input I might suggest he consider long-term care. Many programs have you living in a half-way house, working in the community and basically learning to live life sober and straight for as long as a year.
Just imagine, the kid was stoned through many important developmental years and missed a lot of skills acquired during that time. I've heard young adults say "wow, I've never been bowling or to a movie sober before". They are used to practicing social skills and living skills while under the influence. The year gives them time to learn those things in a safe and supportive environment.
Just my two-cents. I'm a recovering alcoholic and spent lots of time in rehab as I worked my way thru several relapses. What I said above comes from listening to the young people in there with me and to the counselors as the worked with the group.