"Can i set up my fax line on the same line as my telephone line, without any sort of interference??"
Yes - all you do is connect the fax facility you have to your regular landline, just as if it's another telephone.
If you're on broadband ADSL, you'll need a filter on the line, just like on your telephones.
Not it won't interfere - a fax call, in or out, is just another telephone call.
It'll cost whatever the equivalent length/destination telephone call would cost.