"A noise and visitor curfew: fine. But it isn’t reasonable to tell an adult child what time they can come home"
This with bells on. You have every right to expect not to be disturbed by him but to police his movements is just controlling. Of course expect him to be quiet and not disturb you but beyond that what time he gets home does not affect you at all.
Obviously if there are repeat occurrences of him disturbing you or the children then you can look at setting a curfew because he is negatively affecting others in the house but don't just try to control and police him from the start.
I think In the end you'll find 90% of the time he will just crash at his friends places anyway. As a student I would often sleep on the floor/sofa of whoever's house/halls we got the taxi back to even though in some cases my hall/house was on the next street over, literally 5 minutes away, it's just what students do.
Similarly with meals, work with him on how you are going to split them. If he wants to be solely responsible for feeding himself let him crack on with it but set the rule that you always expect the kitchen to be clean, tidy, hygienic and ready for you to use, no leaving Washing up for days or things rotting/out of date in the fridge.
WRT girlfriends staying the night you have to set your own rules for this. You are absolutely right to not want a string of ONS's or casual partners in and out of your house but set some expectation of how long a relationship has to be/how many times you want to have met the partner before they are allowed to stay the night. However don't try and stop him staying the night at his partners place or going back to their places for ONS's, again this is no way affects you and would just be controlling him and his movements.
Again with the music and late nights make it clear that these are not allowed to infringe on or affect you. He can stay up as late as he wants as long as he isn't making noise/crashing around or disturbing anyone else. Make it clear that any music should not be able to be heard outside of his room, he can use headphones or play it quietly.
There are solutions to every problem you've stated they just take discussion and clear expectation from the start. If he is a good kid as you've said he will understand these and it sounds like he already is respectful. If expectations aren't being met you can have discussions and then start to impose stricter rules that may or may not encourage him to move out but don't be controlling for the sake of it.