Lala- I am sure your DS will adjust fine. It will just take time.
My DD likes to talk a lot and that is her main problem. Sometimes she doesn't know when to be quite. In the morning, she didn't listen twice. One for not cutting the picture up, and the second for not putting away things. Afternoon, she did fine. My DH went to visit her at lunch time and she had that look on her face when he showed up, he knew right away she had done something wrong.
He had a talk with her, and she was fine in the afternoon.
I think most kids it is an adjustment, because it is more structured. They don't get naps. Unlike when she was in Pre-K. She had more independent time in Pre-K, so she could just do what she pleased most of the day.
As far as lunch, we put 50 dollars on her lunch card, should last the month. So we will see how that goes for now.