GB's
I hear ya on how many GB's people are at, for I was just in your shoes, and took the 64GB plunge.
If you are not loading it with video then no need for a 64GB. The digital movies that comes with DVD/Blu Rays take up about 2.5GB, depending on length. Pictures do not take up too much room. My Sony eReader books are very minimal in size, so don't worry about books, though I am not sure if the iPad uses more space, so don't quote me on that.
16GB is good if you know all the tricks of air sharing, and such.
32GB is safe incase you add movies.
64GB I think is for people with a huge library of video, music, photos, etc.
My 16GB iphone does not cut it, but I use my 80GB ipod classic as my music source and always will.... Because it's full.