The best (easiest) way to come to Japan is by teaching English. As a musician, I don't think it would be bery easy to establish yourself right away. You could certainly enroll in courses or classes - I don't think your Japanese ability will have that much bearing if you can or can't participate. The more you know, the easier it will be, but taking a class/course will also help you learn Japanese as well. However, you may need to find a fulltime English teaching job to support yourself in the beginning, until you can explore other options.