Your starting move should be to ally Ming vassalize both Haixi and Yeren in your first wars with both of them, and taking one or two provinces at most from each. That way you won't find Ming or in this case a Ming vassal holding some key provinces, or Oirat doing so. Allying Ming prevents Korea from allying Ming then jumping you with Ming. I would take administrative ideas first as colonization is painfully slow at the start and if you want to vassal feed, you won't have the diplo points to tech up fast enough anyways. Trying to colony hop around Africa to get to Portugal and Spain is so incredibly slow with all the tropical provinces that its not really viable. And forming colonial nations in NA is bad because they will be Chinese tech, and easy pickings for the Europeans, and drag you into unnecessary wars.
After that, I would focus on taking out Korchin and Buryatia. Buryatia has a nice gold province which really helps with your income. If you have ADM focus and taken core cost reduction ideas, then you should have no problem coring everything and keep filling out administrative ideas. Your next targets should be Korea and Oirat. Drag Ming into a war with Oirat if possible and get both of them to tank their manpower, and then declare on Korea so Ming can't help Korea. After your first or second successful war against Oirat and Korea (making sure to vassalize Korea once you reduced them enough so that Japan or Ming can't take land from them or vassalize them), Ming will probably unally you as you are big enough to rival. At that point though, you should be big enough to crush Ming easily. With only 20% or so warscore, you can easily take over 100% OE of provinces.
I didn't do this because I restricted myself to coring provinces myself after this and also only taking provinces with claims, but you can eat Ming a lot faster if you take a Shun core and Zhou core, and one or two other unreleased nations in Ming, releasing them as vassals, then forcing Ming to return cores. So each war with Ming should go: take 100% or less OE of provinces with claims yourself, return as many cores as you can to your vassals. Second idea should either be humanist, or influence if your doing a lot of vassal feeding.
All the while, you should be making a beeline through Oirat and the other hordes toward Muscovy. If your lucky, Muscovy is collapsing already, or at least didn't take a coastal province in time to get Expansion first, or even second. If your unlucky, as I was, you have to try to get to the tip of Uzbek and seize their colony once they plop it down, which I did.
If you went the vassal feeding route, you can probably keep your army in the west and eat through Muscovy to get to Sweden or Crimea to Genoa, which would allow your to westernize fast.
Don't reform or form Manchu until its either past tech 15 or so and your military units are seriously starting to fall behind, or your ready to westernize. The horde benefits are too good to give up until you really have to. Ideally, you only want to form Manchu when you can form Qing as well immediately after, and have enough income and ADM banked to enact Forbidden City and Repair Great Wall decision.
My army composition early game was a stack of merc infantry that I used to soak up most of the damage by using them to seige and bait enemies onto them, with a regular pure cavalry stack close by to reinforce when attacked to to wipe out small stacks. Never had any manpower problems and a large stack (10+) cavalry early game will crush all your neighbors armies.
