I think it's a great idea to have a business card as a grad student. It would be really useful for networking. If your school doesn't have a business card printing service you could easily print your own using an online print company.
The same thing is in my mind. It doesn’t matter the roommate is form same department/program or not. People around should be joyful & happy to live in group. Someone who is self-centered cannot be a good option as roommate imo…..