Didn't follow the thread closely but don't complete Stonehenge

You want the failgold to pay for the research no one else is going to pay for (isolation)
Workers chop granaries > chop libraries > cottages.
Turn 65: Whipped 1 Pop for 2nd WB. That way at size 3 I can get out 4th settler working Fish, Crab, and Pig in Wonsan:
Not ideal... 1 pop whip should be avoided when the happiness ceiling is low. Rushing the work boat is wasted as you can't grow now. Chopping the boat would have been better. (And use the pig for growth!

)
Such a city (high food) could have grown to size 4 (working whatever tiles) then 2 pop whip a worker, overflow into a WB (chop to complete) > overflow into library (chop to reach 30

/90) > grow to size 4 again and whip the library.
Wonsan would then have 2 unhappy faces but it can start hiring a scientist at size 3 and another one soon after.
One of the most crucial factors in isolation is how soon can you sustain hiring multiple scientists in multiple cities?
And often raw commerce (cottages) is of lower priority. Especially given a financial leader.
Other important objectives are :
- Sailing if you can make use of the extra food given by lighthouses
- Monarchy if you want to grow your cities, which looks rather nice in your situation.
- Given marble, Aesthetics + Literature for failgold is appealing.
If you can nail The Great Library that's definitely good.
- Alphabet and Mathematics are niche, won't look for that in you game.
- Otherwise Metal casting and beeline Optics while preparing as many great scientists as you can.
A fourth city is not really a priority at that point.
But I can see a good (low maintenance, high commerce return) city spot 3S of Seoul.
It can take the rice from Pyongyang and has a couple of financial lakes to work.
Ideally, the settler for that should come from Pyongyang who could whip it > library (finish with the copper tile)