I also have worked on the Legend as a light tech and also am American, so I needed a visa.
You will need to contact the scheduler and have her send you a letter so you can get the visa. You have to have a Crewmember visa valid for one year. YOu might not need that long but it doesn't cost anything more. The ship will pay you back for the visa. If you are in So Cal you should be able to go to the china embasy in LA. It takes 4 days to get the thing processed. If you are doing it in person you have to also go back to pick it up and pay for it.
As far as the seamans book. I was already on the ship and the ship got us all Bahamian Seamans books. If you haven't already worked for the company you won't be able to get one, because you have to show your training records.
Again talk to the scheduler. I can send you more details if you message me PVT and I can send you my email.