Is the questioner mistaken or correct in his actions after discovering his wife's deception and her misleading him with magic to marry her, and what is the right path he should take after all these events?

If a wife commits immoral acts, then separation from her is better. It is not permissible to accuse a relative of practicing sorcery without proof, for "avoid much assumption. Indeed, some assumption is sin." (Quran 49:12) Searching into a wife's past is forbidden spying, but seeking consultation before marriage is permissible out of necessity. Usury (riba) is a grave sin, and one must repent from it and not return to it. It is not obligatory to return the excess amount unless under duress.