How much ongoing work should I expect for each client?

It depends on the type of service and how many services you offer.

For social media management you might plan content once a week or once a month, with the AI doing most of the work: ask it to generate 30 ideas, approve the ones you like and tell the AI to schedule them.

For a 24/7 AI receptionist, go into the client's account often at first, even once a day, and listen to some call recordings (the call log has a button to play each one). Check how the AI is doing: did it say it did not know an answer, was anything strange, does something in the prompt need updating? Once it works well, check once a week or once a month, or less.

It is like hiring a new employee. Do not expect perfection out of the gate: watch and coach it more at the start, and later your AI employee is an expert that does not need babysitting.