It's up to you whether you want a seperate fax phone number or not. But hooking up the fax is simple, just run a phone line from your wall outlet to your fax machine. I assume you're asking because you have Comcast Digital Voice. There's nothing special you need to do, anything you can connect to a regular phone line you can connect to the phone line provided by your EMTA.
Considering that most home wall phone outlets all lead back to a common point where the E-MTA is usually placed, this will work just fine in most setups. And you're right I don't work for Comcast, if I did my name would be in RED.