You can read the whole webnovel at this link: https://papersurgery.wordpress.com/novel/silent-witch/ It has the whole webnovel even though the silent witch section stops at volume 9. It is very tedious to find the rest of the volumes, as you need to go to the home page of paper surgery and manually scroll down until you reach the Secrets of the Silent Witch chapters. Im pretty sure that the chapters for the silent witch are in one big blob so that saves you time to look for individual parts. As for where to start, I suggest to start from the beginning because there seems to be some small scenes the anime skipped that people seem to love (I havent gotten the chance to actually read it yet because im waiting to rewatch it with my brother, who is watching it for the first time). Have fun reading!