Every round of GPs I made a triple pop with a GS, GE and GA. The total number of GP pops would be the number of landmarks -2 from the Louvre, so thats 5 x 3 = 15 GP pops.
+2 GA from the Louvre, +1 GS from Porcelain tower, +2 GEs from from Hagia Sophia and Liberty finisher, and settle each one. Its very easy to do, you just need to micromanage the GP bars to keep them all equal.
I started the map again to try and better my city development and growth and because the combination of wonders in my capital had given me too many GA points so I couldnt run it in full specialist mode. I focused more with getting my Colosseums and national wonders built faster so I could grow sooner. My progress by 1400 AD was just unbelievable ...
I <3 Korea
I just built the following combination of wonders which eventually gets all 3 GP bars completely equal with all Artist, Scientist and Engineer slots filled (you need a flat riverside capital for the windmill's engineer slot and a garden, marble will also help a lot, plus lots or grassland tiles to settle your GPs on).
In the order they were built:
Temple of Artemis, Great Library, Hanging Gardens, Oracle, Stonehenge, Hagia Sophia, Chichen Itza, Porcelain Tower, Himeji Castle, Forbidden Palace, Taj Majal, Kremlin, Louvre, Brandenburg Gate, Statue of Liberty.
In my first go I put both the Sistine Chapel + Taj Mahal in the capital, but that gave it too many GA points, so this time I put Sistine Chapel in my second city along with various great merchant wonders that I wanted (Mausoleum and Big Ben, plus Colossus since it had 2 fish and loads of water tiles from an inland sea).
To get the first round of great people spawned on the same turn, you need to rush to either education or metal casting depending on whether you need engineer or scientist slots to allow it to happen. You get your first artist slot early with the temple, then I like to make sure I have enough money saved to rush buy specialist buildings past the temple in my capital as soon as the tech is researched (except the Opera house, I get that for free with legalism).
It easily doable on King difficulty using the three early settled GEs. It would probably be possible on higher difficulties, but you might need to use some GEs on hurrying wonders instead of settling them which would be lame for Korea.
If you build all those wonders, then as soon as you have the statue of liberty built and both the Freedom and Rationalism trees filled, you can run all your cities packed full with specialists for the rest of the game, allowing each city to generate a base of around 250 beakers and 60 production per turn (plus loads more beakers in the capital with National College + Academies, and some extra beakers from wherever you settle your GAs). The trick is getting your cities large enough, you have 16 specialist slots in total, so you need around size 20 cities at least that can work enough food tiles to support every specialist slot being filled.