The answering machine portion can be set to pick up after 7 rings (The selectable number of rings is between 2 and 7) or you can do what I did and turn the answering machine portion off. I have a separate machine and don't need two.
No batteries are used. It is powered by a plug-in power adapter and it has built-in memory that retains messages and settings during a power failure without batteries. It works well.
Yes. Standard landline phone service will work. This all has been standardized so everything works together since the 60s. Special services from your phone company might not, but basic calling will.
I've never had this problem but if you have the phone through Comcast cable the problem might be in the cable modem. Try resetting the modem and see if that helps. Also check both of the phone cord ends to see if one of the wires on the plug ends is missing or damaged and check where the ends plug in to see if the contact ends are damaged or out of line..