So this is completely up to you. Several of our advisors have learned to specify how many questions they will answer in the messages in their profiles. This makes it clear to clients that you have a limit, and helps keep their expectations on a reasonable level, as there are some who will try to take advantage and expect you to answer questions all day long.
There are times you will have to be kind, but firm with users. If their expectations are too high, politely explain that they will need to order a new reading to receive any more answers.