I've always struggled with costume, largely because of a lack of knowledge/
visual library to pull from. However, this semester I'm taking a
history of costume class at BYU, and it's helping a ton. It's amazing how, while technique is important, so much of art and creativity is just about having something in your imagination to pull from. I'm a big advocate of not only educating your hands and technical skills, but educating your
imagination. Study outside fields and dabble constantly in new visual material, so that you always have fresh ideas.
These characters are intended to be Nephites from the Book of Mormon. As we don't know exactly where they lived or what their clothes looked like, I've based their clothes on a combination of Greek, Middle-Eastern, and Argentinian ideas. Not that these cultures would have had a particular influence on the Nephites, it just felt like a believable look.