You need to read up on rsync and cron.
cron will execute anything you want (maybe a rsync task... hint hint) at specified times of the day, days of the week, months, years, etc.
rsync will synchronize (or, "mirror") files from somewhere to somewhere else. This could either take place on the same machine or remotely–meaning to sync from one machine to another.
I think once you get a handle on these two simple technologies, you will begin to understand that anything you want to do is possible.
And in fact, get this, there will be no "scripting" involved in either setting up cron jobs or rsync for what you want to do.
Here's a good start. I know it says for Linux, but a lot of it (if not all of it) will apply to OS X (which is a BSD variant).
http://www.mikerubel.org/computers/rsync_snapshots/
You also want to become familiar with making "incremental" backups rather than thinking you need to have several full backups. Why backup a file that hasn't changed in the last year or so?