1. Most rats love to be held and cuddled (and will gladly sit on your shoulder or run across your arms), and will accept treats from peoples' hands quite readily. They're naturally social animals, so are pretty easy to tame.
2. Male rats can have squabbles later in life unless neutered, although many will get along quite happily. Female rats are unlikely to fight, spayed or not, so they might be your best bet.
3. Their waste isn't toxic if touched, but I wouldn't recommend eating it, of course .
To clean their cage, take out the rats and set them on a surface nearby (couch, chair, etc, just be sure to keep one eye on them). Then, empty the bedding and waste into a small garbage bag and tie off the top. You can rinse the bottom of the cage with water afterwards.
4. I used to use dishrags, and my rat would curl up under them to sleep. She did chew on the fabric a bit, which prompted me to remove the rags--I think a lot of ingested fabric-fibers can cause a blockage.
5. Avoid softwood shavings (cedar and pine). Aspen is a really good alternative, as are hemp and Carefresh.
6. They can become attached to anyone, especially if bought at a fairly young age.
7. http://www.quite.co.uk/rats/#Health%20Problems <--Has information on health problems.
So does this website: http://www.ratguide.com/health
8. Usually about 2 years, although some people have reported 3-4 years.

NOTE: All rats are different! Be sure to handle them at the store/shelter/breeder, so you can see how friendly the different individuals are.