The update is currently only hitting the S7 edge units that were part of the company's Galaxy Beta Program, but it's reasonable to assume that the standard S7 models as well as units that aren't running Nougat beta software will also get the update soon.
The update weighs in at around 117MB and also brings along Android security fixes for the month of February. The magenta carrier is yet to update the respective software update pages on its official website.
Yes, they still have this theme.
I don't know the exact name of the dark theme. I was just referring to the one in the screenshot given. Reminds me of the Holo Dark theme used before Lollipop came along.
There are more phones and samsung's firmware is already more advanced with more features and functions that take more time to work on as well. But on 6.0 their software is still ahead of the pack on 7.1