There is no point in doing Express walk-off if using the WDW shuttle. You will not leave any sooner. The busses mostly depart at 9 AM, or sometimes a bit sooner (maybe 8:30) if there are more than one bus for your specific route.
In PC, all the luggage is available in the terminal once the first guests leave the ship. You will not have to wait for the elevator in the terminal, and still have plenty of time waiting for the bus to depart if you leave your luggage outside your room and get it back in the terminal before heading to the bus.