How do I start Casca's story, I only have the option to start work or leave when I talk to her.
Just start working, and it will automatically trigger events for Casca. The only thing is that now, on version 0.3.2, a bug blocks these events and shows only the event of Casca's meeting the main character. If you encounter this, you can send me your save in private messages in Discord, and I will fix this bug manually for you. This has already been fixed in the new version 0.3.2.5.