Is it sufficient to remove the wetness from the hand before wiping the head, and is it obligatory to make up missed prayers when unaware of their number and ruling?

There is no specific quantity for wiping in ablution (Wudu'), and the Sunnah is to perfect the wiping with little water. Wiping the head is obligatory. If there is still wetness on the hands from new water after partial drying, then wiping with them is valid, and it is not necessary for the wetness to reach all of the hair on the head. However, it must be with wetness from new water and not from the remnants of water used to wash other limbs. If the hands are completely dry, then wiping with them is not valid.

If the prayer was invalid due to ignorance of the ruling, scholars have differed on the obligation of repeating it. The majority of them held that it is obligatory, while some held that it is not necessary in the case of ignorance. According to this latter view, you are not required to repeat past prayers due to your ignorance, but you are required to repent for the shortcomings in knowing the rulings of purification (Taharah) and prayer.