I think most of your questions have been answered earlier, but thought I would add from our own experiences on Pacific Encounter to the GBR in late November. When we booked our cruise we chose the 'Plus' (I think it was called) fare, so drinks were included. We usually drink white wine and could each have up to 15 glasses of wine under a ceiling price each day - we never even got close to that amount! But mostly we drank Marlborough Sauvignon Blanc which was very good. Ship's price was around AUD12-13 per glass. I think the name of one we preferred was Kim Crawford? If we ever wanted to buy a bottle of wine, then we had to charge that to our cabin. We did buy one bottle. Think that was around AUD43.
In our cabin, on boarding, was a list of the restaurants included in our fare. We had been rotated through all three - Waterfront, Dragon Lady, Angelos throughout the seven day cruise and we had already chosen the earlier sitting - ours was at 5.45pm each evening. You must either choose early or late sittings before boarding the ship. You can swap restaurants around as long as you give notice. We had downloaded the P&O App on advice once onboard, so no problems there. We didn't like Dragon Lady so opted out of that one. It was so dark in there, the people at the next table couldn't see what they were eating! We particularly liked Angelos, decor throughout was lovely and the food good, although only one menu change throughout the seven days. The pizza eatery was not open at all on our cruise.