To each STB. And it should be the same phone line for all of them (the same phone number), in case you have more than one. The installation and activation can be actually done without the phone line connected. For now VOOM works without the phone line just fine, but the phone line might be required in the near future.
Depends on the installer, most of them will. In the worst case you can always run a temporary extender phone cable if he insists. a 50' phone cable is included.
Probably for PPV and also to verify the location of the STB. Check other threads on this subject.
The VOOM install kit comes with an RJ-11 extension cord of ridiculous length. I'm sure this is so that the installer can plug the unit into SOME phone jack somewhere in the house, completing the install.
You'll pay about $30-40 for a base and jack pair which would give you one phone jack anywhere in your home where you have an AC outlet. If you need more jacks you can buy additional jack boxes for ~$20-25. I got my stuff at HomeDepot.