Yes, hats are allowed at Wimbledon. Take a look at the DM photos.
It's my observation that casual dresses or day dresses, or 'non-dressy' or 'work-suitable' dresses that you could go to the supermarket in or wear on a warm summer day at home are very much an English thing. Americans tend to wear separates. Jeans and shorts would be considered very normal daily/home/casual in the US.
Not sure what you mean by 'boxy'. American women do tend to wear more menswer inspired styles, less peter pan collars, fewer frills, both at work and casually - I suspect it is felt that you will come across as less girly and more serious in clothing that doesn't emphasise the fact that you are female, which still unfortunately equals 'someone whose contribution can be dismissed'.
They didn't disclose the place of birth at the time of the birth because they didn't want hundreds of photographers and members of the public camping out outside the hospital, snapping photos, etc., or making comments if MM didn't leave the hospital within hours of the birth or suffer through ignorant talk about her looking a mess, or otoh gloriously put together compared to KM, etc.
I agree making a big deal out of the privacy of the godparents immediately focused attention on the godparents. I also think the godparents' names, backgrounds, etc should be known.