Find Your Cruise
We did a similar cruise with HAL I hired a dinner suit and accesories, pre booked and delivered to cabin. Once ashore either end it's up to you but I found that going to a restaurant for a meal was enhanced by "tidy" clothes. I did not bother with a suit but relied on blazer and flannels rig both for travel and non formal nights on board.
Dress to match the ship it is lovely you'll feel great.