I've read early reports that make me want to wait before upgrading to 3.13 - things about resource trading, and a visual bug when you can't see what culture (or spy points) a building generates, for instance.
So I'll stick to 3.02 + Solver's patch for now.
(There are plenty of threads on that topic, so let's not derail this one).
As for other pressing topics...
Settling the islands:
Islands so close to the capital would be great, maintenance-wise, but in terms of resources, they suck.
Two new island cities (the two down south of the capital) would bring in one fish, and one Crab respectively. It wouldn't be surprising if, say, Aluminum or Uranium appeared somewhere around there in the late game, but that's a long way away.
Which is why I'd like to explore a little first. See if there's something better. The small mass south of Persia looks slightly greener, while it's possible there might be something better somewhere west. Furthermore, I'd enjoy getting more trading partners, and finding other civs that have not yet converted to Buddhism (or other religion) or only have one or two foreign religion cities (making them fairly easy to convert).
The latter isn't a priority, though.
Adopting Slavery:
That, I do plan on doing ASAP. My initial plan was to convert Mehmed from Judaism to
Hinduism Cosmology, then convert and adopt Hereditary Rule, Slavery, and possibly Organized Religion.
But since converting Mehmed might turn out tougher than expected, that plan is likely to change. It may end up that I revolt to HR & Slavery first, then convert later.
As luck turned out, however, the Raging Barbs are no problem. The only place they can spontaneously generate on the whole continent is that northern peninsula way north of the Ottoman Empire.
Unless a random event brings in a horde, they won't be an issue.
Furthermore, because of the large amount of surrounding islands (big & small map with islands mixed in), I'd be stunned if a civ DoW on the short term. Not until many nearby islands are settled, at least. If one of the close neighbors was rather aggressive, I'd expect it, but not really from those guys.
Regardless, building a proper defense will be important. It's unlikely there'll be war right away, but if the Maya remain this weak, there could be war fairly soon.
On building Chichen Itza in Chichen Itza
Yes. I know, that wonder pretty much sucks. Especially since they should have renamed it "Temple of Kukulcan" when they added the Maya into the game, just like Angkor Wat should have been renamed.
But, because it wasn't... I want it. Just for appearances. The slight culture boost would be nice (but easily equaled by monasteries, libraries and such), the ability to generate a GP for Shrine creation could be nice, but really, it's only because I want Chichen Itza to be built in Chichen Itza, not Istanbul, or Paris, Berlin, or Timbuktu.
Stupid?
Yes.
But this is a story game, not a "how to use the best strategies for maximum AI pownage" type game.
Though utterly owning at least one other Civ is, in fact, entertaining.
That'll hopefully come later on.
OK, maybe not! 
