I'm glad someone is keeping them well. Yeah, I heard they school together although I never had Cardinals since some reason I like the look of Neons better. I kind of like silver stomach. Anyway, like I mentioned before. They would be pretty hardy if you get them from right source. I don't think they are as hardy as Glowlight or Lemon or all those Serpie Tetras but give them right condition Neons can live several years I hear.
I forgot one more thing in earlier post. Please buy them 6 or more, they would be much happier than fewer. They would feel more secure also I believe their picking would be more wide spread. Neons are just like most any other fish that they would determine the dominent fish among the kept group. So they do little spat among them to determine the dominent fish. If you have say 2, the weaker fish is always picked on, but if you have 6, the top would pick any other 5 weaker ones. But generally, once they determine the pecking order and establish their own little territory. They just defend their own patch against the intruder but not go after the other fish in their own territory. Of course, they have to do this again, if the surrounding change. Meaning when you re-decorate the tank. But nothing major, they fight like a sissy nobody injure.
And they would enjoy the thicket of the plants. So keep the live plants if you can. It may not beautiful but they prefer the jungle with some swimming open area although they are small and they can swim through small area. I don't see them "school" since there are no other threatining fish or situation except when I do the water change. Also, they seems to know where is the good spot to catch their food.
Other than that, they do their own thing.
So it may not be such a good thing to see them "school." I know you see them sort of school at the store tank because they usually packed in the small space, not enough space to claim the territory and no place to hide but all open space. So they swim back and forth, left and right. Kind of sad. That is my opinion.
Although I never kept them in big numbers in bigger tank, I don't know if they school if I keep them in such. Will see. I got 55G empty and I can get them 100 when I grow them. Hopefully, I can finish build the canopy and mess with some lighting before they become Neon.(it takes month or so before they develope the neon color. They are little brown fish before then.)