Seriously you're going too deep into the word plot. Nah, not I'm not an ignorant fan lol. Why would he just know ameno? Why would he just know how to float? Also explain his own version of chibi tensei he's only seen madara use a core.
Good questions.. Now here are your answers:
But first of all I don't remember calling you an ignorant fool, if I did I apologize.
Regarding Ameno he didn't know, it just came to him in time of need. Remember when Madara threw that Lighting jutsu at then, he teleported and was surprised himself saying "... so that's what this left eye can do"
He floats only using Susan'no because the goddamn Susan'no has wings, and just like birds can float.
About Chibaku Tensei, didn't he and Naruto use a similar one on Kaguya?? so of course he's seen a coreless Chibaku Tensei before