2. As long as each user has a properly licensed copy of FIleMaker 12 to use to connect to the hosted database, yes.
3. I'm a big believer in multiple redundancy when it comes to backups. You might want to keep back up copies on both a second hard drive and a remote location. Note that your daily back ups to the remote location cannot be done from a server schedule and 3rd party back up software should not be used to make copies of FileMaker Files while they are still open. If you set it up that way, your back up copies might be corrupted by the backup copy process. The solution for 3rd party backup's is often to set up server to backup the live files to a specific folder and then you set up the backup software to back up this backup folder.