So, if I'm using a 7424 to polish the car, should I use the exact same method/pad/polish on the bumpers as I do on the sheet metal?

 

Basically yes. However check the temperature of the parts you are polishing periodically to ensure they aren't getting more than slightly warm to the touch especially if you are using an aggressive compound or pad. They can be more suceptible to heat than metal panels when polishing aggressively.