I am sorry, but according to enotes regulations I am only able to answer one of your questions and so have edited your question accordingly. Your question however identifies the way that Dickens chooses his names and how they play a central role in identifying aspects of the character, even before we have met them.
In this novel, James Harthouse plays the role of a dandy eager to find a new conquest. As shown by the way that he sets out to seduce Louisa, he has no moral compunctions that prevent him from engaging in unscrupulous practices - he is happy to manipulate and use other people, such as "the whelp," Tom, Louisa's brother, for his own ends and purposes, and clearly has no actual romantic love for Louisa. Based on this description, the word "hart" refers to a deer that is hunted, just as Harthouse likes to "hunt" and pursue innocent women, such as Louisa. I wonder too whether "Harthouse" could refer to the inaccessibility of his own heart - it is firmly locked away and cannot be touched. Harthouse is not one to let his heart become involved in his amusement. It is clear that he is a character that never engages seriously in anything, as he has only come to study politics to alleviate his "boredom," and with the way that he so quickly relinquishes Louisa we can see that his pursuit of her was just another diversion too.