It really depends on your expectation. If you are happy with being self-taught and can manage to play the pieces you want to play, then no need to bother yourself finding a teacher. But to me, I prefer having a qualified teacher who can teach me how to play it right, and is willing to listen to my playing unconditionally and gives me comments. Not only does a good teacher teach you how to press the "buttons", but also inspire you and enrich your passions. A bad teacher can kill your passions. So, perhaps, being self-taught and having a teacher give you different learning experiences.
I have been a big fans of Joe Hisaishi since I was a kid after listening to "Laputa" (http://youtu.be/HhL8za8cm7o
). When I learned piano again as an adult, my teacher didn't recommend me playing classical music to begin. So, I played quite a lot of my favorite Japanese pieces - Final Fantasy piano such as "Tifa's Theme" and some Hisaishi's such as "Friends", etc. My teacher showed me all the fingerings and that helped a lot... Then one day, I told my teacher that I was really to play classical.
"Summer" is a very nice one and hope you enjoy playing it. I have the full score and PM me if you are still looking for it.