Great to hear you're looking forward to it. We had an amazing time there.
My answer to some of your questions:
1. I wore a 50s style dress that was slightly below the knee. It wasn't a cocktail dress or ballgown but I felt nice in it. My husband wore a nice shirt and a jacket, but it wasn't his smartest 'wedding' suit. We weren't over or under dressed.
3. When we asked for water they asked if we'd like to see the water menu. I felt a bit nervous and said no thank you. I wouldn't have ordered from it but I wish I'd taken a picture of it! If they still have one, please let me know what it's like.
4. We have only been in the QV room so I can't compare it. The ambience was lovely! It was peaceful and relaxing. At one point I started chatting and laughing with the person serving us and the table next to us joined in so we all ended up having a bit of fun together. It was a great atmosphere.
Anything else? The one thing that surprised me was that despite the price there were still some quite expensive add-ons to the menu. There was one we really wanted to try so we shared it. The coffee was also a real experience, and I now have the same coffee maker, but that was 6 years ago so they might not do it any more!