kjaooo, You've posted your questions under two different cruise lines so I'm not sure which cruise line you're considering; Royal Caribbean or Celebrity. The food is included in the main dining rooms and the buffet. Speciality restaurants have a surcharge. Johnny Rockets on Royal Caribbean ships is $4.95. This fee was put in place mainly to deter the teenagers from hanging out all day in Johnny Rockets which wouldn't allow others to enjoy the venue. Celebrity and Royal Caribbean have many different speciality restaurants to choose from. It depends on which ship you are looking at. Generally speaking the finer dining steak houses and Italian restaurants run about $25/$30pp.
The cruise lines almost always charge double for single cruisers. Norwegian Epic and Cunard have some single cabins. You will set up an account onboard using a credit card and anything you purchase onboard will be applied to that account. Recommended gratuities are about $12.00 per day and that will cover your waiters, assistant waiters, cabin steward, and Head waiter. If you order room service you would want to tip them a few dollars. You actually can get by without spending much at all if you don't drink alcohol or gamble. Soda is about $2 a can plus 15% gratuity. Other non alcoholic drinks coffee/tea/milk/juices are complimentary at meals and they also will have a 24hour coffee/tea/hot chocolate station located on the ship usually up on Lido. Royal Caribbean larger ships have it located on the Royal Promenade.
Dress code will depend again on which cruise line you choose. Celebrity is a Premium cruise line, Royal Caribbean is a main stream cruise line. Slacks are required at dinner, no shorts. Most nights nice slacks and collared shirt would be fine. On the designated formal nights you will see a variety of dress from very formal on Celebrity to suit and tie. You won't be turned away if you show up in dress slacks and collared shirt w/tie. Or for that matter even without the tie.
You may run into some rough waters in November. The ships can handle it pretty well. The Transatlantic cruises are popular and very well may sell out.
You can do ports on your own. However; you will need to be well aware of the time you need to be back onboard and the consequences if you miss the ship.