First Deal Questions

[Chase Luckett]

Hello, I am 22 years old and negotiating my first real estate investment. I live in Owensboro, KY. I have some questions that I would love feedback on. 

My grandparents own a rental property and I am negotiating buying it from them through seller-financing. Because I read How to Invest in Real Estate With Little to No Money Down, I know that the only down fall to seller financing is the due on sale clause. However, my grandparents have the home paid off and their only worry is the monthly rent they were getting to pay some bills. That number is $800/month. 

Details on the home: 1580 square feet, 2 bed & 2 bath, they were charging the previous tenant $750/month (too generous in this market I know)

Expenses: $335/mo on utilities & $800/mo on the mortgage

Questions:

1. What is the best way to find comparable rent rates? 

2. I have a friend and his girlfriend that are starting a family that want to live there. Is friends and family discount viable? I do have other options for tenants. 

3. Is it better to include the utilities with the rent or for me to pay them out of my pocket?

Those are my main questions as of now.