Man Character

Are there any rules as to what objective elements the Main and Influence Character should have?

REGARDING the Objective Story Problem and Solution (and Symptom and Response), the answer is, "Yes, these elements will appear in the characters." The Main Character's objective function will be to embody one of these four elements with the Influence Character embodying its dynamic opposite. Which is which is dependent on a LOT of variables which I won't go into at this time. In a future version of Dramatica Story Expert we hope to have it determine it for you. Until that time, go with your instincts.