Response A: Yes, because there would still be niches in the social fabric that needed to be filled by entrepreneurs in the agriculture field.
Response B: It depends what you mean by "make a good living" > does it mean having what you need or does it mean making 100,000 a year with a 401K?
B1: yes they would make a great living.
B2: it would get increasingly difficult as all your neighbors started meeting their own needs and you had to spend more energy, going further afield, to turn your agricultural products into cash. I suppose transport/sales over internet could help you out, as long as it remained economically viable.
But if you lived in a community where everyone was meeting their needs just fine, why would you need 100,000 and a 401K?