Single rat is okay if you have time to socialize with it.
20 long would be better.
About 3 to 5 years depending on type.
They can be trained not to.
Sort of. Shavings or what have you should be changed out two or three times a week, washing would be okay weekly.
Soap and water fine.
A lot of debate about that now, I don't know.
Engaging little beggars, a lot smarter than mice. Wish I had time for one, but it wouldn't be fair to the dogs and cat, not to mention the fish.