I am just going to respond to part of your question so as not repeat the helpful answers already posted. You asked, "Also, do you think the negative space under the user's photo is to make the feed more digestible (they seem to be like exdents)?"
Yes, definitely! There has been a ton of research about line length and readability. 50-60 characters per line used to be the default ideal line length, although more recent research suggests longer line length (70-80 characters) might be better. I personally think it has a lot to do with the audience, though I have not personally done any research on the topic.The folks behind Google+ gave some serious thought to line length, and more importantly made an effort to keep line length fixed instead of shifting around when the browser window is resized. Here are some good articles about line length and readability to get you started if you wish to learn more: