Well I need to know what to do about my psu because I looked up a calculator and it says 589 and my friends said get a 750w but my teacher says if i can go 100w above or then it will have too much power.
This is untrue. You cannot have too much power. You system will only draw as much power as it needs, no more. A 750w or even an 1000w supply would still be safe.