Is my recitation of the Qur’an valid after performing ghusl following menstruation and before discovering that something else was discharged from me? And am I required to re-recite what I have already recited? And am I sinful for touching the Mus'haf in that state?

If the brownish discharge (kudra) occurs during the period of menstruation, then it is considered menstruation. But if it occurs after it, then it is not menstruation. There is no sin upon you for touching the Mus'haf if you were unaware of the presence of menstruation, because one who errs is excused. Your recitation of the Qur'an is valid, and you will be rewarded for it, for the preponderant opinion is the permissibility for a menstruating woman to recite the Qur'an without touching the Mus'haf. Even if it were said that it is impermissible, you are excused due to error, so your recitation is valid according to everyone.