1. Yes. As soon as you set foot on US soil with the intent to remain here you are a "resident" again.
2. When I shipped our things from the UK, we had a list of items that we had to give the shipping company prior to our move. I had numbered the boxes and then listed the content in each one (very generic - example: Box #2 - CD's, Video games, Box #3 - sweaters & jackets) I just used that same list for US customs.
I think they just want assurances that it's your personal belongings, not new items that you are importing with the intent to sell. You will have to fill out US Customs forms and attach a copy of your list. You should not have to pay any import duty. You may have to pay an inspection fee should they choose to open any of your boxes/containers, but it's a small fee.
Good luck!