Winifred 22

Yes they do take them down when they are sold out. Always double check with the sold out filter button for peace of mind. They do reappear when cancellations occur and cabins become available. I managed to secure a booking once after it was originally sold out. 

It is my understanding no,  unless they are a B C passenger. You would need to dine elsewhere such as specialty restaurant or Kings Court, if  wish to dine with a non Grills or B C Guest which is only fair really on the other B C guests who have paid a premium for their dining. 

They have recently changed the policy at Southampton and the terminal staff will check your arrival time and if you are too early you will be invited to wait in a queue outside until your allocated time. I was 45 mins early and was not allowed in until my time. You will not be able to wait inside. In the past you could arrive when ever but this is not the case now. This was for Ocean Terminal but my understanding is it applies to Mayflower too. Cunard is correct there is no where else to wait other than the queue. Best bet is to visit a local pub or coffee shop and wait for your time.