Definitely self-tech Currency after optics; it'll pay for itself right quick. +1 trade routes per city will be very useful for you; also, being able to sell them techs ought to net you at least a couple hundred gold, and being able to build wealth instead of research would be a small but noticeable upgrade (building research does not benefit from libraries and academies, but building wealth lets you run a higher slider so you have more commerce going through your libraries and academy). Ideally it's a tech you'd be getting in trade. But since Zara Yaqob still hasn't even discovered Alphabet, I have zero confidence the AIs will have Currency and be willing to trade it to you.
Every leader has a limit on how many techs they're willing to see you receive in trade (from them, or from anyone else). This limit is waived if they are Friendly with you or your vassal, but otherwise once you reach that limit they will refuse to trade any more techs to you and give the message "We Fear You Are Becoming Too Advanced" (WFYABTA). However, this limit is initialized at 0 when you first meet the civ. Which means any techs you receive in trade from anyone else before meeting a leader will not increment your WFYABTA counter with that leader. So it is useful to get as many techs as you can out of Zara Yaqob before you start contacting all the other civs with Optics - even techs that don't seem all that useful at the moment. Although you do want to avoid Meditation of course because you need to keep the Great Scientists lined up for an Astronomy bulb, and Archery is worth exactly nothing to you - I guarantee all the AIs have it by now and won't want it in trade, it's not a prerequisite tech for any other techs, and you aren't planning on building archers, longbows, or horse archers.
If you get a settler and found a fairly useless city right on his borders - somewhere like, say, 4N2E of Aksum - then go into diplomacy and liberate that city to him, that will almost certainly give you a +3 or +4 "fair trade relations" relation bonus as well as a +1 "liberated our cities" relation bonus, and push you straight up to Friendly status. At that point (a) there's zero chance he'll start planning to attack you, so that's no longer a risk at all - although if he's already been planning it he may continue plotting. And (b) he's willing to trade any tech to you, even ones he still sees as monopoly techs (such as Horseback Riding or Hunting). 100 hammers for a settler to get that is a pretty good deal at this point in the game. Pass the copper to Thebes, the pigs to Krikav, and Thebes can build the settler in 5 turns which would let you found the city (and start getting monopoly techs off Zara Yaqob) in about 10 turns. That also gives Krikav 5 turns of fast growth, which is about what it needs to grow up to size.
It would be useful if you could give Zara Yaqob a chance of rolling up Currency after his current tech finishes, so you kind of want to trade him Mathematics for something in the next few turns. I wouldn't worry too much about avoiding giving him any particular techs; maybe steer away from Compass if given the choice just to hopefully delay his making contact with other civs. But if you give him, say, Code of Laws, maybe he'll build Chichen Itza for you. Then you'd get the failgold from your partial builds without needing to actually complete it yourself. So there's no reason to worry overmuch about that.
After Fippy generates that second Great Scientist, the balance will start tilting towards Great Merchants. An overseas trade route to whatever city has the Temple of Artemis will probably net you about as much gold as a Great Scientist bulb would net research, but the gold is far more versatile. And certainly you'd rather your non-Thebes cities were generating more gold, because that would let you run a higher slider so your high-commerce capital with an Academy can put more of that commerce into research and get extra beakers that way. The advantage of the Great Scientist is that it pays off immediately, no need to spend 10-15 turns moving the great person to the other city then another 10-20 turns spending the excess gold. If you're making a push for a Liberalism slingshot (which might still be in the cards), two more Great Scientists might be useful to increase your chances of getting there first - one to bulb Education and another to bulb Liberalism. Certainly any of your current cities except Fippy or Krikav, and maybe Fish Man, are never going to generate another Great Person again this game, so you might as well shift the scientists in cities like Jnebbe to merchants instead. You might do the same in Krikav if you'd rather generate a Great Merchant there.
You're about 4 turns from Optics. Then with 100-150 gold out for upgrading 2-3 triremes to caravels, probably another 4-5 turns to Calendar. Fippy's great scientist generation (which should happen in 12 turns I believe - 3 turns running 3 scientists now for 27 GPP, then 9 turns running 4 for 108, plus 165 already) is actually going to be the hold-up on Astronomy. You need to avoid Civil Service until that is done, because otherwise your Great Scientist will bulb Paper instead of Astronomy. If need be (not sure exactly how the timings will play out) you can simply go for Aesthetics, Literature, and/or Music before Civil Service while waiting on Fippy's Great Scientist.