This may sound like a really minor (and possibly silly) feature request, but I'd like to see the download size before actually initiating the download.
Right now, the actual size of a sample project, learning content or even engine updates themselves is only shown when the download already runs.
Perhaps something similar to the small info icon in the library/vault?
I was looking over your post and I thought that this requests sounds reasonable. I have written up a request ( UE-11905) and I have submitted it to the developers for further consideration. I hope that this helps. Thank you for your time and information.