Are customs and traditions, such as a bride's marriage through "Wali Salih Sidi al-Bashir" and her dowry being 69 millimes, and their drawing near to this Wali by slaughtering a sheep or a calf before the wedding, considered Bid'ah (innovation)? And how can one know the legitimate dowry for the wife and follow the Sunnah of the Messenger, may Allah bless him and grant him peace?

The customs mentioned in the question, such as "sacrificing to other than Allah" and "fearing the saint," are polytheism (shirk) that expels one from the fold of Islam. Sacrificing to other than Allah as an act of drawing near and submission is major polytheism (shirk akbar), because sacrifice is an act of worship that must be directed only to Allah alone, as stated in His saying, the Exalted: (So pray to your Lord and sacrifice [to Him]) and (Say, "Indeed, my prayer, my rites of sacrifice, my living and my dying are for Allah, Lord of the worlds"). These sacrifices are forbidden, and their consumption is not permissible. As for fearing the saint in the manner mentioned, it is also polytheism, for fear is an act of worship that should only be directed to Allah, as stated in His saying, the Exalted: (So fear them not, but fear Me, if you are [truly] believers). As for the dowry, Islamic law has not specified it to be little or much, but it has encouraged its facilitation. It is obligatory for those who practice these customs to repent and renew their Islam, with the necessity of gaining deep understanding of the religion, especially matters of monotheism (Tawhid), and performing duties such as prayer, fasting, and wearing the hijab.