It’s my understanding we present ourselves and our luggage at the place you specify above. We then have a 40 minute bus ride to Fusina where the ship will be docked.
It could be pre-booked via TA but not website. If you want to use your shipboard credits, best to wait till onboard.
Price for bus transfer Southampton to Heathrow 160€. I did not meet anyone on board who thought that reasonable.