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Oh, almost forgot:
5. There was very limited internet access aboard the ship. We could just send and receive email once or twice per day. That was it. I brought a lot of books with me on the ship and did a lot of writing, so I didn't get bored, but I imagine most people would. I think a few days is plenty of time to spend on such a ship unless you have a plan to make use of all the down-time.
I crossed the Pacific on a cargo ship last year, 26 days from Japan to Peru, as part of a 3.5-year trip around the world without flying.
I made a video about my cargo ship experience here: https://www.youtube.com/watch?v=uj9yA7KjIuw
A few quick points:
1. Yes, it is very expensive to travel by cargo ship. It cost me about $4,500 total. I'm glad I did it as it was a cool experience, but given the cost I'd be hesitant to do it again.
2. Why is it so expensive? Best I can tell, because the cargo ship companies don't care. Taking passengers isn't their primary business. They're transporting multi-million dollar cargoes, so they probably figure that if they're going to take the odd passenger, they might as well charge a high price to make it worth their while.
3. For anyone interested in how to go about booking a trip on a cargo ship, I explain how I did it and provide a few links here: www.ndoherty.com/cargo-ship-2/
4. Perhaps the craziest thing for me was the lack of security on the ship. My bags were never checked at the port in Japan and the captain told me the door code for the bridge within an hour of boarding the vessel. The bag check when I got off the ship in Peru was also half-assed at best.