Backup to Disk

Hi: easy question I guess, not sure how to setup this:

W2K8R2 server.    Backup exec 2014.    External USB Harddrive 1 TB  need to backup a filer with 700 GB of information

How I should setup this so I can have a better backup strategy?

Full Backup: should I run a full each week?, each Month?

Incrementals, should be daily, but for how long should I keep the jobs?

thanks in advance...