For Stunt 20, it works if you use the railroad tracks too. That's how I first did it because I got fed up of trying to find four next to each other (though I wasn't looking very hard).
And I do remember some of the massive fights, but I can't remember which missions.
Also, specifically for the stunt where you had to shock some guy in the air then thunder drop on him, I just used the basically infinite bad guys in the third district after you power up the last station, but before you recharge the generators. (It's still a blackout at that point and if you don't destroy all the trucks and bad guys on those trucks, you run around forever until you do or you can't start recharging the generators.)