FYI 大きい (ookii) is an い adjective, not a な, so 大きな赤いボール is incorrect. I suspect you know this though since you got it right for the second example, but what you

FYI 大きい (ookii) is an い adjective, not a な, so 大きな赤いボール is incorrect. I suspect you know this though since you got it right for the second example, but what you wanted is 大きくて赤いボール (ookikute akai booru) I believe. And additionally, for な "adjectives" (so to speak, since it's not a direct analog and have characteristics of nouns), you wouldn't just string な with the next adjective, but replace it with で. like, 静かで可愛い人。 But as you mentioned, as far as I understand, the ordering is much more about emphasis than some set rule - to put it with some contrived conversations: A: I saw a big blue ball B: Eh? It was a big RED ball! vs A: I saw a big red ball B: Eh? It was a SMALL red ball! then either ordering could sound natural in context. But I'm not Japanese so I can ask my wife later if that's really the case.