Sounds like its a rotary given the thread size. The first polisher I bought was a rotary used it on my civic paint very soft. You would probably be best of with a da but but you have a rotary.
Best advice take it very slow and easy nothing to aggressive pad and polish wise keep to small sections 18"x18" and work the polish in at low speeds probably wouldn't go over number 3, make sure the polish is broken down just take your time and I'm sure you will be fine take extra care on plastic painted bumpers, i think they retain heat from the polisher more so than the metal panels (someone will confirm) you don't want heat to build up and the polish go up in a puff of smoke followed by the paint bubbling. Done this to a part on my civic that was due to be painted....