I would gently point out that players outside of your guild may not refer to you as "Ser" if you take on the title of Knight as their characters would not view you as nobility, since in Lore, they don't exist.
Doesn't exist? Tell that to Ser Kyrill of Beetletun. Unless someone wants to argue that "Ser" is an uncommon first name in Tyria and Kyrill is a surname? He sounds like a hedge knight to me.