Go to the WJ and get/ask for the 8oz boxed milk every day - would not trust the cooler in the cabin for keeping it cold for more than a day. Way too difficult a question to ask from the shoreside staff.
Many folks ignore/miss the blue link toward the bottom of the app (just below the Daily planner link and just above the links to Safety, Health, Dining, etc) - that lists the dress code for the night.
Welcome to CC.
Forced cabin moves are rare but do happen - cabin changes on a B2B are not that big a deal, more like inconvenience - if you don't get your cabin back ask for some compensation/OBC.
It all depends on how your time and some potential aggravation is worth to you. Assuming you can get price drops easily on an Aussie booking, that is probably worth an exploratory call.