yes you should be able to boot the laptop using the external screen, and here is how you get to the bios to install windows.
# '''Make''' sure the '''Surface Pro''' device is turned off.
# Hold the volume-up button.
# Press and release the power button.
# When the '''Surface''' logo appears, release the volume-up button.
# The '''Surface''' UEFI firmware interface screen will be displayed and you can '''make''' changes.