I don't have a lot of time, but I'll put my thoughts in here as fast as possible.
I'm sure that the ability Imu used is DF related, it makes sense for the "final" villain to have the most hax abilities, possibly a mythical zone one. There's also the possibility that it might be an ancient weapon, but I'll pass on this right now.
Luffy's dream is another hollow mystery that Oda is desperately stroking to keep the audience guessing about something useless and ridicules that we already know anyway.
Sabo probably found out about Imu's target and that's why he went to that Kingdom to evacuate the people. I'm sure he succeeded and everybody is alive and well.
Bony is an interesting development, for me at least, I'd like to see where she will direct the crew and her dynamic with them.