I think Aoda said sama just because Sasuke is higher up than him. Remember Sasuke was able to summon Manda, king of the snakes or whatever. So this Aoda snake is lower in rank, this is saying sama because Sasuke is basically higher in rank since he was using the boss snake as a summon.
And yeah I always knew Naruto never meant to summon Gamakichi, he always summons gamabunta. Seems the first summon available with the chakra requirements like you said is how it works. But that doesn't mean gamabunta is summoned somewhere else, he could just be getting food or something or not at mount myoboku, just how ma wasn't there when pain attacked konoha. No one else can summon toads, it is not foreshadowing anything.
I don't know what to say about Katsuyu, she should have been by Tsunade. We know Katsuyu didn't heal Tsunade, since Orochimaru said she doesn't look so good. So maybe after healing the other kages Katsuyu disappeared because of not enough chakra, I don't see how it could be any other way, Tsunade wouldn't just unsummon her in that situation herself. That's kind of a **** move though...Katsuyu starts healing Tsunade then disappears right after because she doesn't have enough chakra lol. Or Sakura stole her away from Tsunade, which I don't think is right either since Katsuyu didn't seem surprised or angry to be taken away from Tsunade.
