It's hard to predict someone else's bottom. I hope this is his, but my step-daughter doesn't seem to have one. We paid for rehabs while she was under 18-she completed those, but said she preferred living in those places (from the real world). She later did a state-sponsored rehab that she was kicked out of. After a series of arrests, she went to a nicer rehab a couple of cities over. Now, she is living in a homeless shelter, still stealing money for drugs, and going in and out of jail. Her DOC is heroin.
My opinion is that we cushioned her too many times. Family members paid for Suboxone, gave her rides to addiction clinics, gave her rides to methadone clinic, etc. I think you've been doing the right thing with NC and not giving money. We made the mistake of giving her money in the early years, later we made the mistake of gift cards (can sell for drugs).
It's good you are letting him do the research on rehab. He can do the leg work. You don't need to check on him--he's an adult. You don't need to remind or encourage--just let things happen the way they will. I feel like we did too much to help my step-daughter --it went on for 8 years, or so. We are finally all done and on the same page, so that's how she ended up living at the shelter. We love her, and pray that she will some day make the decision to use all the knowledge from rehab to actually make a change. I will always believe there is hope (while she is alive) but we will not give money, rides, research rehabs, etc.