Do your best to keep all the customers happy, both shifts. Get the brothel reputation up. Brothel reputation rises based on customer happiness, and customers that aren't taken care of represent a 0 in the calculation for average happiness.When the brothel reputation (represented on the brothel main screen) is high, your fame will start to rise. Fame is hidden, but once it goes above certain levels, customers will start to visit new areas and jobs.
If after more than 20 turns of keeping the Reputation at High the customers still haven't discovered the gambling hall, post here again, there's a problem.
Yes, in my version it IS important to man both shifts. Try the customer service job. The way it's a little bugged right now (logic error on my part, will be fixed in a future patch), it can potentially effectively push customers' happiness above max.