Currently trying it out on a Indian build, called Just bananas - involving, you guessed it - just bananas - no luxuries, mountains or city states, plantations will only be built when I get my first unemployed citizen and have fertilizer researched. Aiming to get rationalism policies for 2 research for specialists, Statue of Liberty for extra production and the freedom polices.
Because Unemployed citizens are counted as specialists, so have half normal happiness, +2 Science and +2 production, and only eat one food.
And the awesome banana - +4 food and +2 science with pottery and university, unimproved. +6 food with plantation and fertilizer. The maximum theoretical population will be 192, and as working on deity, need 19.375 in happiness buildings.
Should be interesting to see how high I can get in raw terms of population.
Of course, I have cheated outrageously, their is a string of mountains, completely protecting city - only have to fear the modern age.
And some figures for you, looking at 1600 science from the city, about 500 production, and over 200 gold per turn. From one city.