So the student loans tabulate things based on cost of living for the area already. So if you are like me with no parental help you usually take out the full amount or up to 5k lower if you are being frugal. If you are on the more frugal end you can take out more as the semester continues and if you take out money you can return it when you know you have too much.
If your parents are helping with a certain portion, or you are older and have saved up money) whatever you are putting in you can subtract from how much you need to take out.
Average rent depends on your preferences: I paid 500 dollars a month by renting a house with some friends my first few years, I know other people who are renting a luxury appartment for 1200 a month. It depends on your finances. The school gives you around 850 (if you include utilities) to live off of, but you can increase this amount in loans by having a signed lease and going to financial aid.