OP-- I would stop worrying about who should be taking the lead here, and embrace this as a learning opportunity for you DS. Even if he didn't initiate this date, it's good experience for him to learn how to organize a proper date. Have him think about how HE wants the evening to go and then communicate with the girl about it and execute the plan.

Some will have corsages, some won't. You are correct that they are not all "group" dates.

Your son should tell her something like "you buy the tickets and I will buy dinner at XXXX" or something.

You could also have girl (and her parents??) over for heavy appetizers and pics.

If he is not romantically interested, there is not much he "has to" do. He should also tell her that they are going as friends.

This girl sounds VERY controlling. My high maintenance senior DD would not have had all of your son's date's requirements.