Hi SarahS,
It looks like this date has already been cleared to operate, but should there be any change in this situation, you would be informed before the balance is due.
In terms of booking your preferred seat, I understand that you should be able to check in online as you have upgraded. You will only be able to do this once your ticket has been issued and we usually issue tickets approximately 1 month before departure at which stage we will be able to provide a reference number. If you want to book these earlier, you will need to pay the full balance on your holiday and I do need to inform you that once the ticket has been issued it will be non-changeable and non-refundable in the event that you have to cancel your holiday.
I hope this information helps.
Kindest regards,
Julia