halp

I didn't really use any strategy for Trafalgar. I just randomly completed it. (Yes by fluke )

Coming to Three Emperors, I use all my troops to make a quick dash into the enemy's center. The stables there would be your mainstay for the entire camapign. Don't bother to upgrade them. Just spam cavalry and if extra resources do remain, upgrade your cities. And also, upgrade them at the beginning, when your main army is attacking the enemy center.

Now, place your artillery pieces to bombard Vienna from distance. Use your remaining troops to defend them. In the north, DO NOT ATTACK THE ENEMY!! Just block their way and the won't do anything to your Vienna siege. Now comes the main problem. The Southeastern front of the enemy comes alive. I used my Princesses - Sophia, Maria and Isabella and destroyed hem, though with heavy casualities. It's just that you cannot avoid them and they will prove to be the thorn. Fathima would be really useful here as economy is very important

On sieging Vienna, make sure a unit of high health capture it. And then, wrap it up. I prefer to keep Napoleon away from the battleground, and also, do not hesitate to pull your generals back when injured, into one of the cities. Shuffle them and recall them to the frontline, when the recovered sufficiently enough, not necessarily full health.

This is one level I recommend for medal grinding too

No princesses, only Galvez tho. 
I tried to annihilate the initial Austrian Army, and then fall back and let the Russians wear themselves away. I use Nappy for the objective general in the south, and then he just sits on the stable until fit enough to join the fray that is Vienna. Do you have to cap Brunn, or just defeat the general that sits on it? Marmont, Soult, and DeSaix are the best generals france has to offer btw, fight me.

what aout lasalle, davout, and Murat?

For Princess runs, I suggest that you read up first about tips on speedrunning and so on. Once done, I suggest these conquest for the Princesses.

Sophia - France 98 (Under 65 rounds)

Maria - France 98

Fathima - France 98 (Note that Sophia, Maria and Fathima can be obtained in the same conquest. I finished in 57 rounds as France 98 and got all three)

Isabella - France 98 (Only if you have the skill)/ HRE 98 (If you have good generals. Sophia Maria and Fathima will be enough for this. You need 45 rounds for getting her). Even GB 98 is fine. I used the above three Princesses to finish this conquest in 47 rounds. Mopped up 3 rounds later and got Isabella

Kate - Only obtainable by America conquest? (Not sure. Need Verification. Hence tagging 𝘛𝘳𝘰𝘵𝘴𝘬𝘺). Recommended - USA 1775 (See Erich von Manstein's guide)

Sakurako - Maybe US 1775 again. Why? See Erich von Manstein's guide.

Lan, Victoria - I recommend HRE98 for this as it has a central position. But 𝘛𝘳𝘰𝘵𝘴𝘬𝘺's findings (See the formula for rounds thread for further help) has been backing 1806 or 1809 France as it has more industry. littlecorporal has got 850 years for various conquests, but the catch was that he used Lan and Victoria in them. So these three are the only real possibility I see.