Physical Characteristics: At sixteen Edmund is described as being "very well-looking" and "tall for his age" as well as being "well-grown." As a young man he is handsome enough to attract Mary Crawford's interest.
Personality Characteristics: Edmund is the kindest of his siblings, the first one to really reach out to ten year-old Fanny when she comes to live with them. As an adult, he still looks after Fanny (usually) and appears to take his intended profession as a clergyman seriously. He is, however, taken in by the Crawford siblings' charm for a good portion of the novel and allows himself to be convinced to engage in behavior he does not approve of as a result. Most of his poor behavior in the novel can be connected to the Crawfords in some way or another, but Edmund does take responsibility for his own actions, after he recognizes that he has done something wrong.
What to call him:
Edmund - his family
Mr. Edmund Bertram - People who are not part of his family, when his elder brother Tom is around, as a means of distinguishing which Mr. Bertram is the most important Mr. Bertram
Mr. Bertram - when Tom is not around and after his father's death turns Tom into Sir Thomas