By default, Time Machine (that's what you're using, correct?) backs up once an hour. Unless you have a good reason to change it, I would leave that alone. Some people don't want the disk activity running that often (they need to run other programs which require a lot of resources, perhaps), and you can use Time Machine Editor to alter the frequency of backup.
You CAN have other files on the same drive as the TM backup drive - my warning was that, if the drive fails, you've lost both your music/film files AND your backups. For a mobile solution, you could also look at the Time Capsule, which is more expensive, but does mean you don't have to have the Macbook physically connected to it. Of course, it will only back up if you're in your home location.
Matt