I have been able to create a card in Trello and assign members to the card via email. However, I would also like to be able to set card the due date from the same email. Is it possible to set the due date of a card via email, and if so how do I do it?
From what I can tell, no, at least not directly. You might try contacting Trello to request it as new feature though.
In the meantime, you could try a workaround using another free webapp: Trello integrates seamlessly, including 2-way sync, with Sunrise Calendar which in turn automatically adds new events from your Gmail.