Hallow’s End will expire on November 2 at 4am EST. You still have time to complete all the quests and achievements. Maticus has compiled an excellent Hallow’s End Guide that will help you locate where to find all the available quests throughout the world of Azeroth. I am not into doing seasonal quests besides the brewfest, but after checking the guide I decided to go through all the steps. Thus far I have done most of the achievements thanks to the guide.
Make sure to contribute to the wiki page.