As for civics, Free Church is way too powerful compared to the alternatives, and if you're having trouble with relations, make sure to trade techs as soon as you meet a new civ (+4 bonus), start shipping them a spare resource (over time this will improve relations) - preferably for one in return - and hop into any wars that do not threaten you to get the mutual mil boost. In general, if you make sure to have enough military hanging around, the stronger AI will go after the lower hanging fruit, at which point you can dogpile for the relations boost/easy pickings. It goes without saying that you choose the religion of the strongest civ in the game, which is why I don't bother founding an early religion (get those worker techs). As for Mercantilism, I've yet to test it with the (relatively) nerfed trade routes, but every food boost you can get is now crucial with the slower growth, and the free hammers can really help new cities later in the game. I was very happy running it over Free Market in 2.7, as there are already a bazillion ways to get extra trade routes in the mid-game.