I would have to let Kevin say how it would actually work on the podcast cruise but typically, on cruises, you actually select the stateroom (by number), assuming it is available. I knew which stateroom I had months in advance.
As to decks, one consideration I had was not being too high on the ship. The dining rooms on on the lower decks and, because there are assigned dining times for large groups of folks, the elevators (which are not terribly big) get cramed full right before and after dinner. I found being in cat 6 on deck 6 most helpful because we could easily take the stairs down and up from dinner. I only used the elevators to go to the upper decks.