This soup is light and bright. The sour flavor stimulates the digestion and senses. You control the sour flavor here. I like my soup very lemony, so I usually use the juice of a whole lemon and zest. If sour is a flavor that is still unfamiliar to your palate start with less.
Yes, this soup can be made vegetarian, just substitute vegetable broth and leave out the chicken. Though orzo is the traditional pasta this soup is served with if you have a gluten sensitivity simply cut out the gluten and use a gluten free rice or other grain. It will shift the flavor some, but not a lot. Enjoy!