Tricky situation :
- small continent
- not really good neighbours
meaning you're going to be slow teching.
Luckily, the AIs tech a lot slower in BTS, but still I suspect you'll face high teching rivals later anyway.
Optics sooner rather than later may be a good move.
I suggest going for engineering soon. You want your citadels, don't you?
Glancing through these remarks made me consider more longterm plans than most suggest.
I'd say our continent is really small for 3 civs, so even with the absurd variety of this type of maps we can safely presume a larger one across the oceans. Thus a far more suitable than the current one to use as the home continent if aiming for domination.
This ofcourse suggests withholding from expanding over say 5-6 cities here. Such a choise is aided by the fact we ve blocked most land to our use, and moreover that we control most

land of the continent.
Do we NEED more land right NOW?
I mean getting Joao's land would at best mostly retain our tech rate, while getting us more

.

we have no pressing use for. Thus he is a less desirable target.
August's land does have a couple

jewel cities though.
Plus keeping a wonder maker (August) around is not neccessarily a bad thing, and seeing as Joao techs towards optics could provide us some useful tech trades.
Now here's what i suggest:
Aiming for improving current land with an emphasis on teching towards liberalism and through him to astronomy ASAP. The fiery warmonger in me wheeps often over such strategies, but in BTS you have to plan ahead how to rule the world before you introduce it to fire and axe.
I recon some of you worry about uor neighbors bringing the war to us:
3 Prats, 1 Axe, 2 Archers. Sisiutil's got one Axe in Seville. We could definately use a couple more Axes. And I love how Seville's pinned up into the mountains. By land it can only be accessed from one tile, the one closest to Caesar.
Keep in mind his is a chokepoint border city. An army of size 5 with equal defenders and attackers suggest simply a watchful eye. Stil in order for xbows to rid us of such threats, in the near future, machinery is a priority. However them alone can mostly see us through up to knights era.
Along with CoL ofcourse, but no currency. Even if we were to REX and then OB the whole thing would postpone the need for currency quite a while. Plus we can make maximal use of the Theo bulb to get quicker towards liberalism. Bureaucracy early would be nice but not essential. Aesthetics and the GL however stil feel much more tempting.
Disadvantages? Why, yes, obviously. Not going strongly after Engineering and strong trade routes means not showing off the UB witch is a pretty hard task even if aimed properly.

Some hope of making a better job with the UU remains...