Oh but it took me a few lost games to learn this as well

furthermore I had to consult the wiki a few times to get an idea of how it worked best. But now I'm not too afraid of the horde in the first 50 years.
Another good pointer I remember is that they usually close Astrakhan, and/or send you a warning, a year or two before declaring war. This should be your heads-up to wrap up any wars and prepare your scorch earth armies on your borders.
In my game against the Horde I actually pounced on them for the first war. Half their provinces were occupied by rebels and they had problems with some rather huge pretender doomstacks, so it was the perfect time to strike. So waiting for the rebels can also work
Regarding releasing nations; I belive it is a much smarter way to dismantle a huge nation than just taking as many provinces as possible. Of coarse a balance of the two is best, in my Russia game I have crippled the Ottomans a lot by making them release all minors in Anatolia, and this was only in one war.
Making them release minors far away from me means that in the next war it is gonna be quicker to get a higher warscore since now every province I conquoer are closer to me and counts more.(also you don't get infamy for releasing nations)
Ofcoarse A crippled Ottomans makes way for a big Austria, so It might have been a Pyrrhic victory
Time to dismantle the Habsburgs I guess
EDIT: Im playing HttT, I believe In Divine Wind you can just pay off the Horde.