A:AnswerThere is a Ring skill you can activate to pair the doorbell with Echo Show. Search for “Ring” in the Amazon Alexa app, enable the skill, and follow the instructions to pair the devices.
A:AnswerYou can call anyone in your contacts via Alexa, cool ha!
Not sure about shutting off the voice command, when the device is activated by voice command as advertised.
A:AnswerYou mean to use the Echo as a smart speaker to control smart devices, set reminders, create a grocery list, etc? No, you don't need to pay anything because it's a stand alone device. There -may- be a subscription charge for the devices you connect to it (Arlo cameras, for instance). However, those subscription charges are rare and you'll know about those charges when you purchase the device.
I don't know if you can use them without having an Amazon account, so you may need to sign up for one; but there's no charge.