hi, i know there's like a thousand guides and calculators out there, but everything gives me a different answer, asked a few PC repair guys/sellers and they also gave very different answers.
basically i have a friend who has a used 500W PSU-seasonic ss-500et, some said 500W is not enough, others said it's enough. PSU caclulators say i need 360...
his PSU works, no risk in that regard, i'm worried about it being insufficient and ruining the components. i've heard multiple times it's extremely important to pick the right PSU.
Yes, picking the right PSU is very important. In your case, even a PSU with 400watts will be more than enough, since the system will draw no more than 250-300watts under load or gaming.
Your friends PSU is good one, i don't know how much is selling it to you, but you might want to get a new one. Something like XFX 550w is now on sale for $59, which is pretty good PSU and it will serve you in the future if you want to upgrade to more power hungry GPU.