Basically continued doing the very simple things mentioned earlier:
(i) Avoid working unimproved tiles
(ii) Make sure I had enough workers to fulfil (i); and
(iii) Explore.
Got rewarded for exploring when an axe walking through the ice found marble.
As a result, I chopped out a settler whilst I finished teching calendar (which I was researching for the happy boost) and IW (to unlock dye) before heading to literature. Then targeted liberalism and optics (making short detours for music since I had marble and theology to open up The AP). Took astro from liberalism, a choice made easy once I managed to chop in (a late) TGLH in my GP farm.
That aside, all Ive been doing is growing my cities and improving my resources ASAP. Keeping infra limited largely to libraries, universities, forges, courthouses and AP buildings (aside from some wonders) and avoiding happy or health buildings unless absolutely necessary, has helped propel research to 439 BPT. Building the odd market as and when I needed one to maintain the slider has also enabled me to spam twenty cities to cover virtually the entire landmass. Every city has a role to play in the empire, some to provide resources (like a fur city), others can, for example, build missionaries and / or spies after getting the basic infra. Filling the land up like this enables me to avoid building infra in each and every city to raise happiness and / or health in that city alone instead I settle another city and simply raise the happy and / or health caps for all cities.
Just to illustrate the difference that following these basics can make to your game @GGracchus, I put together a couple of metrics from our saves (comparing yours at 1180AD listed first with my save at 1000AD listed second):
BPT: 277 vs 439
GNP: 477 vs 887
Production: 129 vs 210
Number of cities: 8 vs 20
Now lets be very clear, Im not doing this to gloat.
After all, Im certainly no expert: there are loads of players on this forum way better than I am.
Instead, the point Im trying to make @GG is that by simply following some very basic principles, such as those mentioned at the top of this post (and discussed in this thread), you can manage to put together an empire that's larger, techs faster and builds more, very easily. Rest assured, if you can manage to employ the three points mentioned above in your future games, Im certain itll be no time at all when we see you thrashing the AI on monarch and above.
I look forward to seeing you bring your game home.