For me, the big one is comments are now independent of posts, and there's no tree limit. I hope the Steemit.com UI has no nesting limits from day 1. And of course, the 38% reward pool going to comments.
Hardfork's almost certainly not going to be 14th March. They give at least one week from when the Hardfork is proposed. My best guess is they will release the final build (pending bugfixes) on 14th March, with the hardfork happening on 21st March. The same thing happened with HF15, I think, where they delayed it in the last moment without communicating the change.
I wasn't aware of #4 - will check it out!
Yes, I forgot about the 38% going directly to comments, it will support engagement as well.
Also, I agree, it looks a bit difficult to make it on March 14th, but we will see.