Depends if it's there's promotional OBC -those may go away if you reprice. You keep the on board booking OBC if you reprice.
Ask your TA if she offers group rates - those are refundable and could be lower than the regular price.
At the bottom of the main screen, there should be a link to browse other ships - you can set the app to any ship in the fleet for about 90 days before sailing.
Get to the pier after the rush (have lunch some place on land away from the port), typically after 1PM, and do the same on debarkation day (after 9AM). Skip the Key.
For MTD, you can usually book dining times as soon as they are available in the planner (many times 1+ year out). Or, you can go to the MDR host on boarding day and arrange something.
When the kids are out of school (over the summer), your choices are likely limited to Liberty and Symphony out of Cape Liberty. Off season you'd have Odyssey as the choice. You are unlikely to get much a deal on a cabin which holds more than 4.
The app, set to the current sailing (not yours), should show operating days/hours for all the dining venues - they should be about the same on your sailing.