1. The 32S is the classic A321 with the 4-2-4-2-4 cabin in Mint. The 3NS is the A321neo with two Mint Suites in each row except row 1, which has two Mint Studios. The seatmap for your particular flight will show the correct layout. The 3NS is obviously newer so in theory better, but I don't think it is enough of a difference to adjust your schedule just for a seat type that isn't even guaranteed.

2. Do you want to pay to sleep on a plane or pay for a hotel? The service is not materially different.

3. American Airlines > Delta Air Lines > JetBlue Airways, at least for me. AA because they have good food and T8 is super convenient at JFK; Delta because they are usually on time/reliable (though the 767-300ER seats are nothing to write home about). JetBlue Mint is great considering their seats and the food, but if you are collecting points elsewhere it isn't great enough IMHO to jump ship. This is 5-6 hours of your day, not a lifechanging decision. As I said, I would take AA as I credit to fellow Oneworld carrier Alaska Airlines. Looks like you are an AA flyer, so I would take them if I were you.

4. Mint Studio is available only on the A321neo (3NS) and A321neo LR (3NL). If your flight is on a classic A321 (32S) then it is not available. Look at other flights and maybe you will find it, or maybe it isn't operating that day.

-J.