You'll be hard-pressed to find actual viper brand equipment on eBay. They're pretty picky about having that sold only via dealers, and only installed by said dealers.
You will need an actuator in each door to pop them, yes. You can probably just search for door actuators on eBay.
Not sure what systems out there will have the channels you need on it to pop each door individually, I know the 790 (security/remote start) only has two spare channels.