How many days must one fast during the Sacred Months? And is fasting on Mondays and Thursdays of every month the same as fasting during the Sacred Months, or is it unrelated?

Fasting during the sacred months (Dhu al-Qidah, Dhu al-Hijjah, Muharram, Rajab) is recommended, with Muharram being the most virtuous. It is desirable to fast frequently during them, as good deeds are multiplied therein. As for fasting on Mondays and Thursdays, it is an independent Sunnah that the Prophet (peace and blessings of Allah be upon him) loved. If these days coincide with the sacred months, one can combine the intention of fasting them with the intention of fasting during the sacred months.