Q: Is it true that mixing wasabi with soy sauce is a no-no?

A: Not necessarily.  Some Japanese think it is more sophisticated to put a dab of wasabi on top of the sashimi or Sushi before dipping it in soy sauce.  It depends.  If wasabi is freshly ground, then you might want to try that way to enjoy the flavor more.  But it is totally fine to mix wasabi and soy sauce together.

Q:Is it true that I have to eat Sushi in one bite?

A: Again, it depends on the size of your Sushi.  Originally each Sushi piece was made in a one-bite size so that you would not have to break it with chopsticks.  However, Sushi served in the states tends to be a bit bigger and especially rolls can be huge, so you need to use chopsticks to break them into bite size portions.

Q: Is it true that Sushi can be eaten by hands?

A: Absolutely.  However, it is wise to use chopsticks when you are dealing with a large Sushi piece or one covered with sauce.
See how to use chopsticks at the Japan Guide site (http://www.japan-guide.com/e/e2039.html).

Q: Is it true that there is a certain order to eating Nigiri-zushi?

A: No.  Eat as you like.  Some Japanese say Sushi should start with the omelet Sushi, but it is not necessarily true.  Enjoy!