Does voluntary fasting, such as on the Day of Arafah and Ashura, suffice for making up missed days from Ramadan, and what should I do about the remaining day of make-up?

The days you fasted voluntarily do not suffice for the obligatory day that must be made up, because a non-obligatory act does not fulfill an obligatory one. You must make up the day you missed. If you were unable to fast at the end of Sha'ban, then there is no expiation upon you. However, if you were able, then in addition to making up the fast, you owe an expiation for delaying the make-up, which is one mudd (750 grams) of food for a poor person. There is no objection to observing voluntary fasts before making up what you owe from Ramadan (definition).