I’m going to a Gala at an academic conference. I have never been to a Gala before - what does one do at a Gala? What does one wear?

Here are some dresses I’m considering:

With a cute cardigan


Other suggestions are welcome - my style is a little 50's for dress up clothes, and I wear a 16/18.


I also like this one - but it’s a wee bit too much for me:


I should note that this is a queer conference - so I don’t think it will be understated.