Which hard drive size for an old desktop PC?

Hi everyone,

My old desktop is almost full. It has years of photos, videos, and some game files, and I don’t want to delete them. A new PC costs too much, so I want to just add a bigger drive.

I’m still learning about this. While searching, I came across Orange Hardwares, where you can buy desktop hard drives in a lot of sizes. But I don’t know which one is right for me.

Is 4TB too much for a normal home PC?
5400 RPM or 7200 RPM, which is better?
Is a hard drive still okay for backups, or should I get an SSD?

Thanks! Any tips will help.