HAHA, thank you. I'm flattered lol. Here are my guesses.
1. Jack hit a woman on his way home, and he carried her all the way home. So that's the corpse in the living room.
2. Jack killed his girlfriend (wife?) Lenore (maybe she cheated on him) and covered her with the blanket.
3. Jack lured some girls to his house and killed them to feed the corpse flower.
4. Jack has dual personality or paranoea, he can't tell reality from illusion. His bad aspect took control and killed those girls. That's what Jack calls "dream".
5. Jack is a scientist or something, he runs a secret lab and studied mutant spiders and plants, and fed them with human flesh.
I think that's all for my hypothesis. And I have some questions in my head.
1. What's the meaning for the "beep beep jack" scene? I think it's from the movie IT. But why?
2. What happened to Lenore?
3. Who's the previous owner of the house, why is there a key hidden in the sofa?
4. The spider seems to be in Jack's imagination, what does it stand for?
5. Those books shared the same word "four". What does it imply? I initially thought it would be a password for some puzzles or so.
Sadly, The movie itself doesn't help much in understanding what's going on.