Now i am learning how to stop the unhappiness in Republic. Once i change to Republic Government, i disband 2 out of 3 army so i dont have to pay for shield support. I normally have a temple ready in each city, but still not able to stop the unhappiness. Its annoying. lol. Civ is more than unhappiness. lol. I think the temple isnt able to stop the unhappiness when the city has 5 citizens. I have to play some more and see how each happy wonder will decrease the unhappiness. Colloseum is too expensive in the mid game, dont you think?
Colloseum is expansive and I build it usually after marketplace, bank, stock exchange and harbor. By that time I have enough income. Important to control hapiness is to set enough of your workers on the tiles with the most arrows and build roads around your city to get more arrows. And get those 3 traderoutes. I don't build temples (perhaps others do) to control hapiness problems. When needed the luxury rate will go up (not to far) and other wise it will be elviis. After building Michelangelo's you can go for J.S. Bach..another great wonder for hapiness control.
You're last question I have to think about. Do you have any hapiness wonders jet??? Get to Democracy quick will also help a lot...