Basically, I made it my priority to play tall in the early-midgame and grow the city as large as possible from the very start, and to that effect (almost) everything went my way (the single exception being that pirates kept pillaging my sea amber, fish and clams, and early game naval warfare is almost sheerly a question of production (and good rolls, which I unfortunately almost never got), which I couldn't match with only one coastal city (and a small, relatively hammer-poor one at that). My attempt to found another one cost me some time because an
enormous barbarian invasion from a nearby city which is not cost-effective to take swept in and took it. Fortunately this shouldn't be an issue for a while since I just researched Rudder and now outclass the pirates for now.
Anyway, that aside, even though I know what I actually did to make the happy and health capacity of the city greater, I'm honestly kind of at a loss why this never seems to be doable in my other games. I deliberately chose to play as Minamoto for his trait combo with this aim in mind, but that only helps so much, or does it?

This is also my first time several games that I decided to play RI Planet Generator instead of Totestra, and it does seem more generous with resources even with the default settings (and also doesn't throw me a damn jungle in literally every settle in place BFC), which obviously makes an enormous difference.
But, I also got really lucky on a few pretty major things, as well. For instance, I managed to get the Theater of Dionysus
and wine, the event with the population sacrifice for +2

successfully, and also the Great Work of Science which reduces epidemic rate by 5%, all of which add up to a huge increase in growth capacity which agrarian farms can feed up to. Otherwise, I got Stonehenge for the pagan temple

bonus, and the trait combo of: Monarchy, Traditional Custom, Serfdom, Merchant Families, and Paganism might be one of the very most effective selections possible for maximum happiness by the early medieval era, with the caveat that the economic civic is more or less immediately irrelevant for this purpose, and that if one doesn't get Stonehenge, a state religion mandating civic would be equivalent, though to top it, you'd have to take Caste System instead of Serfdom for the additional point of

which cuts your food supply shorter. Traditional Custom and Monarchy in particular is absolutely massive in this respect with +2 from Palace, +1 from Walls, -1 unhappiness from mutual exclusivity with Autocracy, and the bonus to Local Autonomy which already provides +1 of its own!
At first I was somewhat disappointed with how granular this mod has made happiness, and how harshly scarce it is in the early game if you don't focus on developing it, but now it's a feature that I particularly enjoy for being so engaging, variable, and contingent upon a multitude of things which are liable to change and also not reliably certain from game to game. In vanilla BtS I would just overgrow cities and whip the useless angry citizens (which are basically just reserve hammers anyway since their unhappiness poses zero risk or complication other than the opportunity cost of the citizen's lost labor. When the Slavery civic already so efficiently converted food into hammers, overfed angry population was actually
more valuable in many cases than content working population anyway. That makes the civic even more ridiculous than the concept of converting them instantly into buildings and units. In this mod, if your people are unhappy, you can't just execute them for profit; not only will you lose their profitability from labor, they'll riot and destroy your costly buildings (made all the more precious by the fact that you actually had to build them from your content population's labor) and separatism will skyrocket and threaten you with losing the city. That is a much, much more engaging and interesting system than that they just sit there willingly lined up to be mulched into cement or drafted overnight as crack troops (who are suddenly willing to die for you again!

).
The other thing too is that by the time you can get to Monarchy in vanilla BtS, all you have to do is spam garrisons and your happiness problem is more or less permanently solved for the rest of the game, and that solution works almost every time. As long as each additional point of population brings more value than -1

/turn for its unit maintenance, it's worth doing from an economic standpoint. Obviously, you're not always going to be building garrison units (and other government civics might be a better choice in any particular scenario), but for the purpose of this particular problem, it doesn't make for especially interesting gameplay because as a solution it is so one-dimensional and consistently effective.
Back to RI, though, my capital is still poised to grow further. If I can manage to get more resources, it certainly will, since I still haven't even built a Monastic Order yet, which will net me an additional +8

, when I'm already capped with +7, not to mention that I'm not far from getting windmills, and could theoretically replace my mines with them soon, but that wouldn't be a good idea from a gameplay standpoint since the new population would be unemployed citizens and I'd only lose production while throwing food into the wind (or rather, getting it from the wind

). Since I am running Serfdom and now the irregular units are approximately as good as their contemporaries for the era, I am liable to face some absolutely enormous SoDs spawn instantly, so that's a real danger, and also, growing further doesn't even really do me much good at this point owing to limited specialist slots, but in spite of that I'm actually determined to see how large I can make my capital so early. Later in the game once Craftsmen start getting more productive than the land and more abundantly available, it will surely become an awesome industrial center. Also, I think Agrarian is my new favorite trait now.
We'll see how it continues, but even if I end up losing the game, I am still really pleased to have made this achievement, even if much of it was due to luck, and this will be a memorable game in any case.