i've never had happyness be a problem before health after i research calendar. there are so many happy resourses that open up once you have calendar, and then there's the markets and forges that make most of the happy resourses double their effectiveness, and temples are always an easy sourse of a few extra happy faces. then once i get drama, happyness is never an issue. if too many cities are bordering on unhappyness i just dump another 10% into culture, and all my cities gain another 2 or 3 happy faces (1 from the culture, 1 from theatre and sometimes one from colloseum)
happiness and health both become an issue at about 25 population for me. but by that time, its only realy GP specializing cities that need to grow any more and the drama national wonder takes care of happiness probelms for one city completely, and who'd realy want more then one super GP city.