The first one was more to get a feeling for the situation and goals, and the second one to actually get the goals. I did cheat during the first attempt, as I was going to miss UHV#2, but wanted to get a feeling for #3 without redoing the beginning.
The starting situations overall were rather similar, with Mukden being a well-established city, China controlling its historical territory, Dzungaria being five cities, and Mongolia one. Korea was similar in both games as well, and as would be apparent later, France was the major European player and rival for tech lead. In the first game, China was relatively weak, not having built any shrines, and a worse city placement. In the second game, China had both Shrines. In both it did not manage to get Porcelain Tower (maybe it should?) and the Forbidden Palace (It probably should not.). In the first game Korea had Himeji Castle, and in the second one China had it.
Silver Tree Fountain was built in Turfan in both cases. I did not use it, but that is my fault, as it definitely should be used. 3-4 great generals can reasonably be expected during the conquests.
Regarding Civics, in the first game I went with Despotism - Caste - Syncretism - Bureaucracy - Regulated Trade - Hegemony. (I captured a few workers from Korea before switching out of Slavery.

)
The rationale is that Hegemony is greatly helpful during the conquest, and around 30 cities will be captured. Syncretism and helps with culture and food, Caste is great as always due to all these plantations and the production boost to Weavers and Jewelers. I kept Despotism because the alternatives were not any better, and at least it can be used to get a few units, and whip fresh conquests, to use the population that would otherwise starve. I did not use this enough in this first game. I went Bureau + Reg Trade to maximize my capital. Now this was a lapse on my part, as obviously they would scale badly in a 30 city empire. Bureau is defensible, as the alternatives are not that good, but Reg Trade is definitely a mistake, as that comes at the cost of merchant trade, which offers ~ 90

/turn from trade routes, vs. ~45 /turn from Reg Trade, resulting in a relevant economic benefit, and much more importantly doubles production on markets, which are important for UHV #2.
Learning from this, in the second game I went with Despotism - Caste - Syncretism - Theocracy - Merchant Trade - Hegemony.
I replaced Bureaucracy by Theocracy, as an experiment, because Caste already boosts Priests, and the additional happiness could be helpful, especially when whipping my initial cities. The additional production does not hurt either.
In both games I settled my two cities 2E of the deer and 1NE of the northern millet.
In the first game, I conquered Korea first, then China in its entirety, capped Vietnam and Burma, the Tibet and finally finished with Dzungaria, finishing up on the deadline. Finishing with Dzungaria meant that I could not profit from STF.
In the second I went after China first, capturing what would become my Core, taking the first turn to get espionage to check if Korea was indeed weaker than me. Then I signed peace as Korea foolishly attacked, easily conquered them, went after Dzungaria, capped Tibet, which had controlled a city in Dzungaria, then went for Mongolia and most of Southern China (now independent as China had collapsed without its core), and then captured Vietnam from France and capped Burma on the last turn. Not having experience with it, I did accidentally obsolete STF before getting any great person from it by trading for Geography.
Note that while China is not significantly behind in power one should whip before attacking, as reduced population means reduced military strength. Also fights should be picked in an order such that useful units are obtained first (heavy cav > bombards > firelancers > anything else).
In the first game I was generally unfocused, doing a bit of research initially, not whipping and just building generally useful buildings in my new conquests. These were all huge mistakes. This caused my shortfall on UHV#1 in the first game.
From the beginning anything that is not focused on UHV#1, i.e. building units, should be focused on UHV#2. This means no research, no science buildings, and a focus on cultural multiplier buildings (theatres, (maybe Estates and Civic Squares, but these are quite expensive, i.e. for cities that have nothing better to do.), and if you got Himeji Castle, Walls and Castles). If applicable, Walls and Castles should be built first of these, as they are rather cheap and come with double production from Stone and Hegemony. The UB is good, but expensive and should probably come after these buildings. Then science infrastructure (universities, lighthouses, post offices).
While (not) researching I did try to get a few techs to boost my economy. Key techs are civil rights for Individualism, which I wanted to adopt rather sooner than later, Optics for ocean trade routes and geography for the additional trade route. While I would say that these are not critical for UHV#2, they do speed it up. Achieving UHV#2 earlier means more research into UHV#3, so it is a significant bonus. If not researching, the only option on how to get these is obviously trading, as there is no reasonable method to get enough espionage points for stealing.
That said, espionage points should be concentrated on good techers, as even one stolen tech can make the difference for UHV#3. This concentration should happen rather early, to get the points without running the espionage slider.
Anyway, I got UHV#1 on deadline in both games, now on to focusing #2. Note that this is a "by" goal.
I discussed the buildings above, so what remains to be done is the population goal. First, the Vietnamese capital does count as China for the purpose of this goal.
Then there are a few locations that should be settled in my opinion. Basically Taiwan, as it has a few resources and is a solid spot, and the Shandong peninsula, as it can use the Korean pigs and Fish.
Hainan and 2W of Vladivostok are fillers to get over the line.
Other cities can grow as they want, if more population in China is needed, the cities outside China can always be whipped.
Regarding civics, Individualism is good even when working on UHV#2, as it does greatly increase the generated commerce at the cost of about 10 pop in China and Manchuria (~20 plantations). This 10 pop can be found elsewhere, especially new cities, should the need arise. Free enterprise clearly wins over free speech when it becomes available, and constitution is clearly better than theocracy. In my second game I did switch to Individualism as soon as it was available. In my first game I neglected adapting my civics, in a further error.
That this is a "by" goal means that it can be completed at any time when all three conditions are met. Since here we want to tech as much as possible, it is beneficiary to complete this goal as soon as possible. This requires balancing the culture and gold generation, as well as keeping an eye on population and possibly a settler or two in hand. Note that the 19th century plague can hit just before the deadline on this UHV, but that should not be too impactful, as the population will roughly decrease the same amount everywhere, even increasing the effect of new cities. In my second game it hit a few turns before I got the goal, but it was no problem. In my first it only struck after the deadline. In my second game I completed this goal 4 turns early, with

lagging a turn behind

and population being fulfilled by a long time and around 0.3 percentage-points margin. I did run artists in my first game, but not in the second.
In both games I did trigger my first golden age as soon as it was available and the conquest was done. This GA gets buildings done and helps generating

.
At around this time the most significant event that was out of my hands happened: France collapsed to core in the first game. This greatly weakened the major competitor.
In my first game I made a major civics swap into Individualism, Free Enterprise and Colonialism after getting UHV#2. The first two are explained above, and I did the third, because it cost no additional anarchy, reduced maintenance slightly (there are colonies!) and better options were not available at the time.
In my second game, I did a triple switch into Constitution, Free Enterprise and Secularism when I could. Secularism easily beats Syncretism for research.
In both games I did get a second GA from great people on top of the GA from UHV, but with STF another one is in the cards, and maybe even without it with a bit of planning.
Note that from the UHV#2 deadline to the #3 deadline are 25 turns and for #2 25000

will be in the treasury, allowing 25 turns of research at -1000

/turn. In my first game I had around -900, and had spare cash. In the second game I had around -800, but completed the goal 4 turns early, meaning I had little spare cash. Anyway from then on, it was 100%

all the way.
The research strategy is simple: trade as much as you can, but not with the ones that lead. 2 for 1 trades are no problem, as the competition is not with the civ in fifth place in tech, but only with the first placed one.
For the techs to be researched, the usual applies: The AIs love the top of the tree, so go for the bottom. Priorities are: Physics for observatories, and whatever gets the civics. Later on Electricity for permanent contact and a slight

bonus.
At this point cities should only build buildings that increase the total science output when compared to building science. Every bit counts!
In my second game Mali collapsed around 15 turns before the deadline, cutting of a trade for ballistics.
These events out of my control, and my better playing in the second game, lead to the first game being significantly behind in tech. At the turn after the deadline I had only 116000 tech points in the first game, but 138000 in the second. In both cases this was right at the top. In the first one, I formally go tthe goal, passing France the very same turn, but Germany passed me in the interturn and was 1000 points ahead. In the second game France was at 136000 points and I only passed them with the tech I researched in the interturn and thus did not actually get the UHV (as some of you probably guessed).
As closing comments I waant to state that this clearly deomstartes the viability of the goals at normal speed and Monarch difficulty, implying viability for the Standard Normal/Regent settings.
As there was a bit of discussion on the strength of China, I want to say that I would prefer a stronger China, bith militarily and economically. Economically, because that is more buildings to capture and militarily because that is more units to capture. That is, unless China has better military techs. Especially Musketeers would make conquest of China much more difficult. Cuirs would be annoying but no big problem.