PrinceofLightning I can put up to 150 chapters in draft and schedule them for the next 5 months without any problems. I never encountered any bugs that caused my drafts to vanish. Not even once.
Also, I would recommend that you do NOT write on Inkstone. I write on Microsoft Word, and then copy/paste the chapter into Inkstone as a new draft. This is to prevent problem such as a sudden severance of Internet connection, and I'll be able to check spelling and grammar with Microsoft Word, and I have a backup copy.