Who should pay how much for rent?

What is "fair" is what he decides that you pay to live in his house, so as being a landlord is a job where you earn money, pay taxes etc so a business relationship. Based on your take on renting, all my tenants would be living rent free as I own my houses they are living in so I pay no mortgages and according to you that would be "fair" but it is a business relationship, my job so I can earn a salary and pay taxes and they were not the ones who worked hard, saved hard, didn't spend money to have the latest cars or meals out instead I put my hard earned wages into property, it is me who pays for all and any repairs, not them so a fair rent is what I offer and they accept and if they don't accept then they are free to look elsewhere to rent something else

You both should split the utilities 50/50. The question becomes what to pay for the room. I would find out want the going rate for a room in a house costs. Look on craigslist.

What he pays for a mortgage payment doesn't matter. He could pay less or more then the market rate for a room.

No idea.

Take a look at the general cost of renting a room in your area, and go from there.

What ever the 2 of you agree on. He can charge you what ever similar rooms are renting for in your area.

that is one of the MANY things that you both would need to have in writing PLUS the costs of all things that you will split, like: utilities, cable / satellite / food, etc etc.........if everything is not in writing, then there may be hassles later :)

If you use the house equally, you pay half. Because you have a smaller bedroom means little because during the day you use as much as he does of the rest of the house. Maybe pay a little less but half the utilities. If you have problems now, it will only get worse. Maybe don't move in.

unless your also paying the taxes, homeowners insurance and utilities, you should split it evenly.