Regarding flares, in MW4 the flares were generally useless... But they did 0.1 damage, or something like that.
I used to run a joke mech, which was an owens cranked to max speed, loaded with as many flares as it could carry. I'd just run around and spray flares all over an enemy mech. I actually managed a few kills using only flares against mechs with stripped head armor.
The one useful thing about flares was if you learned the location of the camera in a mech, because if you stuck flares on the right location you effectively blinded the pilot.