Is limiting oneself to the fard (obligatory acts) of wudu after ghusl for menstruation sufficient to validate the prayer, and if not, must the missed prayers be made up if their number is unknown?

Ablution before ghusl (ritual bath) is a confirmed Sunnah. However, covering the entire body with water with the intention of removing ritual impurity is sufficient for ghusl. If you washed the parts of ablution once, some scholars have stated that this is preferable. As for limiting oneself to the limbs mentioned in the verse of ablution, without rinsing the mouth and nose (al-madhmadhah wal-istinshāq) and wiping the ears, this is contrary to what is most preferable, and the Prophet, peace and blessings be upon him, performed his full ablution for prayer when performing ghusl. The ghusl you performed is valid and does not need to be repeated, but you omitted some virtues that should not be omitted in the future.