The answer you should be looking for is that they backup every night. You should also keep an up to date copy of your site on your computer to be in the safe mode.
Most Internet Hosting Companies use some combination of equipment and software to ensure that the servers are up and working, that is very much important.
would they charge you extra for the domain names or since it all goes to one site will you be charged just for one.
You need to find out who to contact if you have a problem with billing and what is the process for solving problems.