Overextension

[River]

Since playing with the new expansion, I found that overextension is incredibly punishing. Hence my advice: IF you find yourself over a 100% overextension after a war, load the game, and try some other peace treaty that avoids this.
above a 100% overextension is EU4 launching god mode to make you more or less lose the game. (about 160 in revolts, all my merchants are absent, prestige, legitamacy and army tradition are down the drain, money is gone... you get the idea).
so Load

[shoki]

The peace screen will tell you how much overextension you get. Add this to your current one and you know if you are above 100%. As you pointed out it's bothersome to be above 100%, because you get many negative events then. But it's not impossible. In my last otomans game i was over 100% many times and only had a few revolts.

[Kagemin]

If your nations is stable otherwise you can get by with ~160% overextension once in a while, as long as you take care to let the uprising progress tick down in between. Going above 200% is where it usually gets really ugly, but if your army is big enough you can survive even that (if you can focus on dealing with it at least).

And yeah, as shoki said, you can at all times see how much overextension you're gonna get.

[River]

true true, I could've known what my overextension would be (so, it was my own fault), but I didn't expect the backslash to be that impressive. But having a stable government, and a managable 'unrest' helps a lot. Ottoman is pretty good with that, Dai Viet a whole lot less. moreover, with Cham, Khmer, Laotians, Borneon's and Min's under you, revolts jump up like mushrooms. Worse, instead of just one garrison of 20 appearing you got three of them. Hence, if you have 5 revolts of 60 rebels each... it can get really hard.
the negative events I can deal with. it's a pity that everything goes down the drain, but you can easily rebuild this with two wars.