Here's the thing about boundaries that is very very difficult: they aren't rules for him to follow, they are guidelines for you to use to help you navigate situations that are unacceptable to you.
Going over them with him is not only unnecessary, in many cases, it's just asking for more trouble.
He will continue to cross your boundaries whether he knows about them or not. What's really important is that you have a plan for what you will do when that happens.
That being said, a lot of people feel like upholding their boundaries is somehow blindsiding the person who trespasses over them. So I understand that you might feel it's just common courtesy to let him know what your boundaries are. I think if you are going to tell him, you can't go in there with the expectation that telling him is going to change anything about how he behaves. So really, figuring out when to tell him depends more on you and when YOU will be ready to tell him what your boundaries are and then let go of whatever he chooses to do with that information.
Does that make sense?