Must I make up the days on which madhy was discharged after impermissible conversations during Ramadan, along with feeding a poor person, and am I obligated to adopt the Maliki school's opinion on this matter?

You are obligated to repent from the forbidden relationship by abandoning it, regretting it, and resolving not to return to it. As for fasting, you are not required to make up any fasts nor offer expiation. You are also not bound to adhere to the prevalent madhhab (definition) in your country, and it is permissible for you to act upon a fatwa (definition) from someone whose knowledge and religiosity you trust.