With my homeland filled, it was time to start expanding out to the islands. While scouting for that, I popped Aesthetics from a hut on the west island! :) I do believe this is the latest tech I ever popped.
OK, so I've got a minor economy crash going on here - I actually dropped from 50% research to 10% research in a single turn! But that whipped courthouse at Uppsala will get things right back on track.
Also, finally one of the work boats met another boat floating by. Hello Brennus! Unfortunately, he had Hinduism, so religious conflict seemed inevitable, and Open Borders (to enable foreign trade routes) was off the table.
In the next several years, and actually throughout the whole game, my capital would build every single settler and worker for the whole empire. Once it got its granary, Nidaros could literally grow every single turn, and the only way to stop the out-of-control tribbles was to make it build food-consuming units instead.
Meanwhile, I wanted the Pyramids too, but it was too late. Other wonders were more important; I just couldn't get the Big Triangles with the Colossus and Hanging Gardens also both underway.
Genghis Khan then showed up. Tech trading and Open Borders were both available. He's ahead of me to the tune of Construction and Alphabet, but lacks my slingshot techs of Code of Laws and Metal Casting. I flipped CoL for Alphabet, but he wouldn't trade Construction yet.
I then contacted Louis of France, and he's ahead by a dazzling array of techs but unwilling to trade any.
And I got my second Great Merchant in 475 AD. After some careful studying of the lightbulb list, I researched Currency and Monarchy, so he could do this:
Naturally I revolted to Bureaucracy right away, and Org Rel in the same anarchy period.
With my homeland filled, it was time to start expanding out to the islands. While scouting for that, I popped Aesthetics from a hut on the west island! :) I do believe this is the latest tech I ever popped.
Finally Louis demanded tribute - I forget what but I paid it right away - which brought him up to Cautious and amenable to tech trades. He was researching Civil Service, so I flipped it to him for Feudalism, and to Khan for Literature and Horseback Riding.
With the western island city, and the culture expansions from Sid's Sushi, I was finally able to get a trireme to make the jump over to Mongolian territory. That boat contacted Gilgamesh over there too, then finally Justinian as well, completing the roster of rivals.
And 
I also expanded to the east island and immediately spread the corp here as well. The island cities would receive first priorities on expanding Sid's Sushi. The corp is a bigger boost up the growth curve for a brand-new size-1 city, than for my other homeland cities that have grown themselves to size 6 the traditional way and can take care of themselves for the moment.
You can also see in that screenshot that my research had headed for Optics. Going through Compass was important to get harbors going (the culture slider and Hereditary Rule fixed our happy cap, but health was tight at the moment). Going through Machinery was also important to send Berserk escorts out to the islands. And Optics is natural for an archipelago game anyway.
With Optics, I sent out two caravels right away to make sure I got the circumnavigation bonus.
In fact, I researched the entire bottom line of the tech tree first, which is quite rare for me. I almost never research any of Machinery, Optics, Guilds or Banking, which all usually just wait until I can get them in trade for something on the Education or Construction lines. But these techs were the right move here - the Grocer and Bank were very immediately necessary at my corporate HQ.
And speaking of the caps, Louis turned up with this delicious variety of resources to sell me. Very helpful!
In an amusing moment, I brought a berserker-settler pair to this island - and a barbarian city popped up ONE TURN before I was going to settle. (Note the 5% fortify bonus on the barb archer.) Well, the berserker easily took care of that, promoting himself to Medic to heal quickly and knock out the second archer too.
By the way, here's a shot of my capital.
This is definitely the earliest I've ever had a size 20 city, by something like a hundred turns. And it's still got TWENTY FOUR surplus food, meaning it's going to reach something like size 32! Sid's Sushi is crazy. This game is absurd. Well done, Sullla. 
In other news, Louis had researched Paper, so I directed all my espionage at him until getting research visibility, to see when I had to worry about the Liberalism slingshot. I panicked for a moment when he went to Free Religion, then realized that was thanks to Shwedagon Paya.
And in other other news, one of my exploring caravels found a barbarian city with two fish resources. This looked worthwhile: two berserkers and an executive (and a to-be-captured worker) were a cheaper raiding party than the usual settler-berserker-executive-worker combination.
By the way, Sullla also did awesomely in picking the Vikings for this scenario. The Trading Post is splendid for an archipelago map; it's like having the Seafaring trait from Civ 3 with extra ship movement. Berserkers are a natural fit as well, speeding up conquering the barbarian cities, especially with the free Aggressive Combat promotion. And the Financial trait makes all the water tiles nicely worthwhile to work, especially with the Colossus or Golden Age to turn it on for Ocean tiles too. This adds up to a perfect storm of suitability for the scenario premise.
I'd not realized this would happen, but my second city (Uppsala) produced a Great Prophet thanks to the Oracle. He built the shrine for some more help in the cash department, helping me float above 50% research. And shortly thereafter, GP #4 spawned as another Merchant from my capital. His best use seemed to be to settle there for the +12 gold after multipliers.
So while researching Astronomy and expanding out to all the islands, the variant rule of no expanding the corporation unless you're at 50% science, took center stage in my gameplay. To achieve compliance with this, the key wasn't economic growth in general, but managing the slider specifically. This meant adding raw cash whenever possible, which I was doing in the form of merchants and the shrine. Adding commerce would only contribute towards raising the slider by whatever small percentage the commerce exceeded the city and corporate maintenance costs of generating it in the first place. Adding raw cash directly boosted the slider. And each new city whipped a courthouse the instant it became possible (almost always when the city hit size 6), since that directly cuts expenses to also allow raising the science percentage.
A key component of that angle would come a bit later with Corporation technology. Losing the Great Lighthouse trade route would cost me more than Wall Street would gain. But the trade route is commerce, while Wall Street generates pure cash. This combination adds up to net economic loss, but a net slider gain, which is the key for the variant rule. I'd finally be able to push the science slider back to 50% and finish spreading Sid's Sushi to the last few cities that didn't get it.
So 
I pushed research through Education to Economics next, reaching it in 1390 AD. This was very important on two counts: one to get into Free Market to slash corporate expenses (from 359 to 269) and boost trade routes, and two to start a Golden Age with the free Merchant. The GA would even let me adopt Free Market for free, and I also picked Pacifism. I didn't need the Org Rel bonus while building units (settlers, work boats, executives), and the new cities didn't even have Confucianism anyway, so I might as well take the lower upkeep and get some extra Great People.
Towards the end of that Golden Age, Brennus came along asking me to return to Org Rel. Okay, sure. I'm in GA so the change is free, and plus I'd just cashed in the Pacifism bonus anyway with another Great Merchant in my capital.
And as we approach 1500 AD and race to grab cities and sushi, here's a neat little tactical puzzle:
In 
the picture, that galleon just dropped off a stack of settler and executive that want to build a city on purple dot (it'll expand to reach that fish before 1500 AD). But there's no military unit in the stack, and there's a barbarian archer there. There's a berserker coming from my next city to the south, but it's still three squares and three turns away from the city site. How do we guarantee that the city gets founded on time next turn? Answer below the picture.
Answer: Load the berserker into the boat. Every square that the archer can possibly reach next turn is adjacent to the sea, so the amphibious berserker is guaranteed to be able to reach the archer. :)