In this case, it is natural to put it into the beginning of the sentence, like: "Прежде всего, мне интересно ..." or "Прежде всего, хотелось бы знать ..."
Now I see why it was hard for me to understand your English sentence "what made you start studying Russian to begin with" - first I thought "to begin with" applied to "studying Russian" and then I realized it applied to the whole sentence instead!
You're welcome! But actually it is accusative here: "ответить на вопрос". Prepositional would be: "Мы говорили об этом вопросе".