2). Your point of entry will be Newark. You will need to clear immigration, claim your bags, clear customs, and recheck your bags. Given recent lines, I'm going to bet you will miss the connection.

4). The US does have a $2 bill but is more of a novelty. It's not typically used for everyday purchases.

5). Small marks on bills are not a problem and shouldn't cause any issues.

6). It is my practice to say business if I have any business related activities in my schedule. Mark business, then state you are there for a conference and some tourism. You have the appropriate visa for this. I frequently combine business and tourism and have had no problems with this approach.