From my experience of VB in the winter months, express isn’t necessary at all. You’ll only need it for the aqua coaster, which seems to still build up a small line even on slow days. You can also use your Tapu Tapu to place yourself in the queue from your cabana which is pretty awesome, but I’d imagine you won’t need to use it much as everything should be walk on.
While the luxury of booking rides from your cabana may be sparse, please take advantage of your cabana attendant bringing food & alcohol to your cabana. You’re going to have an amazing birthday!!