What do i need to do to extract several faces as their own object from an existing object?

see object merge node in documentation

You'll need a Group SOP to create a group of those faces, then in your other object, place an Object Merge to pull in that object and group.

There's also the extract shelf tool on the modify shelf. Select faces, tab->extract
Note that it doesn't remove the selection from the original object, it creates more of a 'duplicate' that references the original.