Hello, nice to have you with us 
There is a lot of stuff you can do outside Wanikani and it will not only depend on your current level of knowledge, but also how much time/money you want to invest. E.g. do you want to study completely on your own or go to a class or even get a private tutor?
Here is a link to a different forum that suggests a lot of other material besides Wanikani for reading/listening/writing/speaking.
Think about what your weak points are and where you would like to improve And find something you enjoy, e.g. you mentioned reading books. There will be lots of material suggested. Just try out different things and enjoy it 