It doesn't really matter what user it's ran as (though, obviously, running things as root when you don't need to, while not harmful in this instance, is never a great idea). It gets all of the settings from osTicket.
Yes, you'll need to configure osTicket for receiving incoming emails.
See the documentation here for more info: http://osticket.com/wiki/Email_Settings#Routing_Incoming_Emails(http://osticket.com/wiki/Email_Settings#Routing_Incoming_Emails)
There are several ways to do it, using cron.php is just one of them.
I would actually recommend email piping if you can do it. It's much simpler.