When going for a culture victory at what point should I switch the slider to 100% culture? I'm thinking quit research after obtaining Liberalism for the Free Speech civic. In an ideal case, it would be after getting music, Liberalism and Nationalism for free. However, if you do not have any of the multipliers including the Hermitage built, then the 100% culture is not doing anything valuble for you. In compatitive xOTM's the winning player goes 100% around 1000 AD and will have all of the techs needed and a several religions.
Is there a preferred economic civic? I'm thinking Mercantilism for the additional specialist. This really depend on the difficulty level since in higher levels where your culture cities are big and the Ai cities are huge, Free trade will likely give you the most. You can trade education, Liberalism and Nationalism to get to that tech. In lower levels where you were able to build so many wonders and the AI cities are not that big to get good trade routes, Representation powered specialist will likely keep you ahead tech wise too.
Religions: Found your own (risk being a heathen) or adopt the religion of others? Again level dependent and also the accessible naighbor dependent. At lower level do as you wish but once at Monarch and above see who is around.