Looking back, I would have done some things differently, but I have no way of knowing if it would have mattered.
It's never to early to start setting and ENFORCING boundaries. Remember, boundaries are for you - what you will and will not tolerate, accept, etc. It's not about his stuff, it's about YOU. For example, I have a boundary that I don't want to smell cigarette smoke in my house, therefore no one smokes in my home. Period. Doesn't matter who you are, you can go outside if you feel a need to smoke.
Good luck, hugs from mom to mom
Cats