Guise means appearance. One can appear as something else by changing their appearance or "disguising". A guise is how you appear, a disguise is what you wear to change your appearance. So, you can say the same thing in two different ways. "We wore the guise of a cowboy - He looked like a cowboy" OR "He was disguised as a cowboy - He was dressed like a cowboy." Guise can also be figurative. You can appear as a friend. He came in the guise of a friend. He appeared as a savior. His savior's guise fooled everyone.

Depends on the context, but yes. "Guise" could mainly mean "identity" or "version of oneself".