There shouldn't be any sighting of a completed Space Battleship Andromeda in this series. (though a plan for it maybe) It was launched in story for the second film/series. So it won't be ready the first time Yamato comes home.
I hope to see Kirishima again though. I half expect it to fire a nice parting shot to a Gamilas warship with its bow cannon.
As for Niimi. I too think there is a connection between Kodai Mamoru, Sanada, and her. They are all around the same age (late 20s). A friend of mine speculated that if things had gone another way, she'd be Susumu's sister-in-law.
From what little we know of Chapter 5 at this time, I suspect Episode 17 will be the Yamato 2199 version of the Space Fortress episode, where we got most of Sanada's backstory in the original. Though I don't know what will happen to Niimi and the others after the mutiny (Shima will live, but he could be in the "dog house" with the Captain and crew for this one).