No advantage with the firewire 800 port, footage from tape is always imported in realtime. You will need a 4 to 9pin cable unless you are using a firewire hub or daisy-chaining via a firewire hard drive.
No specific settings required, but review your Import preferences. Create an Event, create a Project and click 'Import from Camera.' The import dialogue will default to your webcam, so choose your camera in the left-hand column and click Import.
The main purpose of Compressor is to export your finished project in different formats for different distribution purposes. Read all about it here:
http://www.apple.com/finalcutpro/compressor/