Without a doubt, clarify not only your concerns but become firm within yourself and to him what the rules are in your home. But have no expectations, and protect your valuables and your energy.
it has been my experience that if I step in to provide a soft landing for my grown child, she will not take FULL responsibility for her own life. If I soften the consequences of her choices, even a little, I am doing her no good.
I need to be honest and strong, courageous enough to risk discomfort for a time and see that I often do these rescue missions to make MY anxiety and parental guilt go away. I dont want to feel the feelings it brings up in me, so I take an action that feels better in the moment.
In the long run, I end up with resentments because she was not grateful enough, not you-name-it-enough, to have changed as I see fit.
For me, the codependency of parenting is the hardest work to heal through. Fortunately, I don't have to finish today!
Good luck in your situation. It sounds like you will have many golden opportunities for setting firm, clear boundaries. My only advise is to prepare for that now by coming to terms with yourself as far as what you will accept in your house and what the consequences will be should the lines be crossed or disrespected.
Or, change your mind now. Don't go forward with the plan if you don't feel it is right.