Re: Kage VS Kage
1a.) Why do people think that Naruto and Bee are going to show up, Naruto PTSD, lol? :D They're busy hunting down the white Zetsus, and the way Kishi's writing the manga, he's compartmentalizing everything, so I think they'll not be written in way to interfere. They're also sealing Edo Tensei's along the way, so they're kind of busy, and really this is Naruto's training.
1b.) Unless he has his TBB Rasengan complete and knows it won't blow everyone, including his friends up, I think he's best used in his current capacity with Bee overseeing him, which would be harder for Bee in a fight against the Kages because he have to focus too much on them due to their deadliness.
2.) I figure only the shown reinforcements waiting for the signal are going to make an appearance, and only notably the sand siblings but maybe a couple from another village like the Ao of the Mist or nins from the Cloud, but that seems less likely to me unless Kishi has plot for them that I don't know.
3.) This fight is dangerous, especially considering it's just begun and only opening jutsu were used. If it wasn't a desert, the place is going to be obliterated when this is over. As it is, even the desert is taking a hit from those dust release jutsu, and they were just openings. Thus, reinforcements have to be carefully timed to avoid injuries and casualties, just as Shikaku said when sage mode Naruto fought Nagato, that sometimes the best team work is staying out of the way because they're on another level.