Wow, that's a long time not to have been on a cruise.
You will see a very big difference in the ships now compared to the Rotterdam V, which I gather was the ship you were on 25 years ago. I loved that ship and sailed on her many times. Zuiderdam is completely different - we've only been on her once and had a great time.
What are your ports? This will help in suggesting excursions.
You can buy wine in Florida and take it with you to the ship;
order it through Ship's Services 1-800-541-1576 or check out HAL's website "On Board Gifts" - right hand column main page.
If you buy it in Florida and take it to the dining room, there will be an $18.00 corkage charge and 15% gratuity. I believe, but am not sure if you buy it through HAL, they only charge you the 15% gratuity, which it charges on any drinks you buy in the bars, including sodas.
A sports jacket and tie are fine for formal nights, but a dark suit might be nicer. It's up to you.
As there are no longer informal nights, (where men were required to wear a jacket), now it's only Formal and Casual/Country Club Casual nights. He will not have to wear a jacket, like in the "old days" on the nights other than formal, so he may want to take the suit.
Can't help you with Open Seating as we haven't tried it yet - we always have late main seating.
Have a great cruise and come back and tell us how you enjoyed it.