Correct - no dessert party.
Monsieur Paul and a few other restaurants have prix fixe events- think $200+ per person for a fixed menu.
If recommend Rose & Crown or Teppan edo. The problem with Via Napoli is that the Italy Pavilion has a DJ and could be difficult to get to. We did Rose and Crown one year and loved it. No special menu but it was great. If you do Teppan Edo, I'd book it later in the evening. After dinner, hang at the deck outside the restaurant on the second floor. It's slightly obstructed but few people know about it and it's away from the crowds.
We're eating at Yachtsman then going to the park. You run the risk by going to the park later in the evening or leaving and coming back. I highly doubt you get turned away due to phased closure. That typically only happens at MK, but it could happen this year. With all the construction at DHS you're limited to two parks rather than 3, so the crowds are gonna be insane (worse than previous years I think.) we've been there so many times that we're willing to take the risk.