From the outset the code looks ok. I would leave the Change and Query methods inside the class. 

If the class does get abit too much then `partial` the class into sensible files. Also, as a side note, look up [SOLID][1] it will help you to break down and structure your code if appropriate.


  [1]: http://www.c-sharpcorner.com/UploadFile/damubetha/solid-principles-in-C-Sharp/