What does the monster's 'monster' qualities and physical stature tell us about himself and the other characters in the story (especially Victor)?
Good question. First, if this is your first reading of Frankenstein, you might have been surprised to discover that Frankenstein is not the monster but rather the scientist who created him. Secondly, you might have found it interesting that the monster is described as quite human looking, not the standard "Frankenstein" one sees in cartoons and most film versions of the novel.
So, what are the monster's "monster" qualities? Mainly, his inability to speak or walk well at first, and then most importantly, his monstrous deeds--the violent murders, especially of a child, the threats, and his vindictive pursuit of revenge. You could also discuss the Monster's ability to be ubiquitous--he seems to be everywhere, watching and stalking Victor and his family.
Many readers have asked why Victor made the monster so large. There are several reasons for this. It makes the monster seem invincible; Victor's experiment is not able to be physically controlled by its creator. Next, the monster's stature represents the scope of Victor's quest. Victor builds the monster to satisfy his hubris. He wants to be recognized by mankind for his accomplishment. In other words, if one is going to do something, go big!
The effect of these monstrous qualities upon the book's characters is mainly upon Victor. As the novel progresses, Victor, who looks normal on the outside, becomes more monstrous on the inside. He takes on the monster's qualities, but no one can see this, just as they cannot see the good traits of the monster because of his exterior. Shelley includes these ideas to demonstrate the disparity between appearance and reality.