The sit-down dining room is a much better choice than the buffet. If you are cruising on the QM2 you should really bring a dark suit.
Cunard has a tradition of formality. For example, afternoon teas and ballroom dancing. Not sure if it is still offered however, they used to have fencing lessons.
FYI, the passengers on the QM2 tend to skew older.
Personally, I love the QM2 however it is not for everyone.
Also, I have not sailed Cunard post COVID so not sure how service and food quality has fared. Pre-COVID I thought service was good in Britannia and the food was OK for dinner. I haven't sailed Princess but from what I have heard the food is better.
I have sailed obstructed balcony. If you go for balcony, I would spend the few extra dollars for an unobstructed view versus obstructed on your honeymoon. The one caveat is that a balcony may really not be worth it in November. Due to the cold, you might rarely use it. If it were the summer, I would say absolutely yes get a balcony.