Its personal preference,I prefer the front of the ship, less engine noise, but some people prefer midships and some do like the stern, once you've done more cruises ( and you will ) you will be able to judge for yourself. While you are on explor the other decks at different times etc to see what you think. In relation to breakfast theres always a setady flow so dont rus, you could also order breakfast in your cabin if you want, and if you miss breakfast by having a lie in, theres always food and snacks around all day, just dont rus, my favourite crusie saying is 'theres never any rush' just relax. Sunbeds, always plenty of them and in different places, more noisy round the pool area, quieter at the bow and stern. Crusing is dangerous, you get hooked, ask anyone. lol. You'll love it.
The best part of the ship depends on you as a person. I would always recommend a Mid/Mid ship cabin. This means you are half way up the ship and in the middle of the deck. You will feel the movement of the ship less in these cabins. Your cabin number does not matter when it comes to shore excursions as depending on your excursion you are given times to meet regardless of where you are. Breakfast timings really depend on what restaurant you are in. If you choose buffet breakfast there is always space to get in. Waiter restaurants, you might want to go in early to beat the rush. Sun-Loungers are plentiful, again days at sea will be busier around the pools, the rest of the time you should be fine. I hope you have a great time.