Q: Should I learn to read music?

Yes, if you want to be a serious musician, a capability to read music can
be very useful. There are many good musicians who cannot read music, so
reading music is not strictly necessary. However, music notation is a very
widespread means of communication, and an ability to read music will open
up worlds of information. The many different systems that use arrows and
numbers that exists have their use in explaining specific harmonica related
things and for absolute beginners. However, they are generally considered
not to be a good alternative to ordinary music notation. They are much more
limited, and no other musician will be able to understand them.