I actually tried this challenge today (first challenge I guess), and it was not as hard as I expected. Playing v1 and on King difficulty with 7 other civs.
I was lucky enough to start on the biggest island with the Mongols and Aztecs and I conquered both of them pretty quickly and also got the MapMaking tech. All the other continents were fairly close. Basically I just started a few cities, and kept an eye on what the other civs were doing, establishing embassies and steal technology with diplomats. At the start I was in depositism at 100% tax and when I got republic I switched and probably was on 20% lux and 80% tax. My economy was incredibly good so I bought most cities. Germany was on a rather small island and I managed to buy two of their cities, before moving onto Leipzig which was size 15 with walls, took it down (took me a long while, many units died), and after that for some reason everything fell into place. Chinese were arriving on my island but I drove them back and attacked their continent. Romans were a joke, so were the Zulu's. The Indians had only a a size 3 Delhi when the game finished at around 1800AD, pretty odd. Very fun challenge but a lot easier than I expected, finished with a 97% score and topping the Powermeter from start to finish.
What I thought was pretty funny was that in 1800AD my strongest units were the catapult and knights...very strange