If you are considering such a long cruise on a line you have not sailed, I think it would be very wise to take a shorter cruise on that line first.
As you noted, there is an added bonus of an on-board discount, and, if you pay with an AMEX platinum card, other extra goodies. You might also look for a TA affiliated with Virtuoso, which adds their own amenities (cocktails, a complimentary shore excursion).
Take a 7-day Radisson cruise to experience it and book your honeymoon on-board.
Just my advice