I agree with the locked door issue. Just bite the bullet and say it bluntly: “It is not acceptable to not lock our door. I am concerned about theft and worse.” Post it notes are passive-aggressive. Yogurt cups and stuff being on your side of the room are small beans and indicative of a bigger problem. Choose your battles.
I also think @lookingforward has a great point. I am a little concerrned that you might let your new freedoms go to your head. This is not judging, but you need to consider that ANY roommate might be uncomfortable with what may be perceived as promiscuity. It’s perfectly fine for you to want to have a lot of sexual partners, but it isn’t reasonable to assume that any roommate, no matter how open minded, is going to be okay with a lot of different guys/girls being brought back to a shared dorm room over the course of a college year. You are not going to be able to keep it a secret for long, either in the dorm or on campus.
This is a total parent thing to say, but you need to not only consider your reputation, but that of your roommate, any roommate. Sorry, but there are plenty of people, even at college, who will try take advantage if they think something is easy to get, and if they know where to get it. It puts both of you at risk. If you plan to be as sexually active as you imply, then I strongly suggest you save sexual encounters in the room for the people you really care about. Quickie hookups might be best left for non-dorm locations when the opportunity strikes.
I am changing my tune a bit, given the additional feedback you’ve given us here. Yes, you are entitled to bring people to your room when a roommate isn’t there, but I think it’s important to consider that multiple random people, who may not be known well, could in fact steal things or just turn out to be not very nice people. Not very nice people, who you don’t really know, could do anything in your room, including things to your roommate’s side of the room, that you simply can’t predict.
I agree that you seem to be doing the compromising in your current situation, but I also think you have some unrealistic expectations about how much freedom college brings you. Going to college, where you will be living in shared quarters, does not mean you suddenly get to do everything exactly the way you want to do it. You still have much to learn about being a responsible adult and respecting the needs of others.