What is the ruling on delaying the fasting of a vow, and is one who fulfills a vow rewarded, and does fasting extra days beyond the vowed days have the same reward as the vow or more, and is Zakat al-Fitr or expiation due after completing the fasting of a vow?

If the vow was made before puberty, then its fulfillment is not obligatory. If it was made after puberty, then its fulfillment is obligatory, and its maker will be rewarded for it. If one vows to fast certain specific days or for a specific period, it is not permissible to delay it without a valid Shar’i (Islamic legal) excuse. Delaying it without an excuse is a sin, and it must be fulfilled along with an expiation for breaking an oath (kaffarat yameen) according to some scholars. However, if there is an excuse, there is no sin upon him, and he must fulfill it. If the vow is general (not tied to specific dates), then there is no harm in delaying it. Being cautious in religious matters and doing more than what was vowed indicates the perfection of faith and is rewarded.