why pixels look so tasty... 🤤

a 650W would be happy with that, I'd recommend trying to grab the 16GB version, If you're on Linux you can just turn the PC off unplug old GPU and put in new one, Windows is abit more tetchy, I'd recommend looking up DDU Display Driver uninstaller tutorials so you don't have weird driver gremlins 😉

gives you a bit more wiggle room, but I'd still avoid something like an RTX 5070 as that's really pushing it or an RX 9070XT, you also prob won't have the PSU cables for 2x8 PCIE, What Graphics card have you got your eyes on?

You need to check What PSU (Power Supply) you have, if it's a 500W you don't want to be straining it with anything too hungry, and from a software standpoint I'd recommend downloading and reading how to use DDU (Display Driver Uninstaller) apart from that you're golden