Is ghusl sufficient for the discharge of madhy, or is wudu' required after ghusl, and is one wudu' sufficient for the discharge of madhy and prayer?

Pure water is sufficient for removing both minor and major ritual impurity. Wudu (ablution) is included in ghusl (ritual bath). So, if a person performing ghusl invalidates their ablution during the ghusl, they must repeat wudu after completing the ghusl. As for madhy (pre-seminal fluid), it does not require a special wudu, but it does invalidate wudu. Wudu is only obligatory due to it if you intend to pray. A single wudu is sufficient for all instances of impurity.