Just switch to another fire group that doesn't include them, and they'll stop firing. FYI.it's irritating that you can't stop them when they overheat the ship system
Overheating is another subject, and fairly complex. You could help a little by putting the Thermal Spread experimental on your powerplant. But with 4 beams on a Viper...it's gonna get hot yeah. Maybe replace the 2 medium hardpoints with multicannons -- less power draw, and good against hulls.
Now I just built myself a turret boat, a T10 with nothing but turrets and a fighter, so I'm not against turrets. But putting them on a Viper isn't such a great idea. You kinda need all the firepower you can get, and turrets are weaker than gimbaled.
Anyway, do whatever's fun. You'll get practice in any case, and learn how to control turrets.