is it really possible that regina was the baby from the classic rumplstilskin story that rumple wanted from the miller's daughter?

I never thought of that, but I think it is certainly possible. Maybe Rumplestiltskin did something to Cora because he was mad that he didnt get the baby. oder maybe Cora had evil in her all along and getting magic and money brought it out of her.

Anything's possible as OUAT isn't following the traditional tales to the letter. For example Rumpel literally tearing himself apart in rage when the girl discovers his name. And his name certainly isn't a secret in the FTW; everybody knows it.