I prefer everything to be how you would read it as text. So create_file_dialog it is. Honorable mention is to have it namespaced in a class or something which I think is best. file_dialog.create or dialog.create_file or even dialog.file.create
I agree. I say open door so the function should be named openDoor.
Honestly nowadays none of that matter if you're using any remotely modern IDE with good indexing and a sensible search, you can start typing however you mind works and it will find it no matter how it's named.