prepare for a long post:
First conecern is population, here is how I micromanaged your cities tiles to maximize population growth:
Concern #2: Happiness:
You shouldn't have taken any of those cities from Polynesia, you should've simply focused on growing your initial cities, taking those cities from Polynesia costed you a lot of happiness that you could've used towards new Carnivals. and don't think about any future offensive wars, at least until you get Prachina's and you can go attack someone kill their military off, then take as many luxuries as you can get in a peace treaty, therefore getting you even more happiness towards your next golden ages.
Focus on building/buying Temples to get happiness from the celts religion. Focus on buying/building Colosseums and then building Circus Maximus to allow for population growth.
Concern #3: Military
You don't have enough military to DEFEND yourself, let alone go and attack anyone. After you increase your happiness again, focus on getting a decently sized miltary so you can defend yourself.
I see you have a research agreement coming in 20 turns. Use this to push you through Printing Press so you can get Zoo's. Spend the 20 turns researching Compass + Prerequisites to Printing Press, and start researching Printing Press right before the Research Agreement comes so that it can push you through Printing Press.
I would then research Astronomy so that you can build/buy a caravel in Salvador.
For Social Policies, I would take Landed Elite as your next policy so that you can grow, and then jump into Aesthetics, it will be critical to helping you with your planned culture victory.
Then I would go into Order for your Ideology and take these Tenets:
Level 1:
Hero of the People
Socialist Realism
Young Pioneers
Universal Healthcare
Level 2:
Academy of Sciences
Cultural Revolution
Worker's Faculties
Level 3:
Dictatorship of the Proletariot
If you have extra policies after that, go into rationalism to help out your science, so that you can keep up with the ai's.