If you look at your current hard drive using a utility such as Tree Size, Folder Size or similar you will probably be surprised by what you see.
I would be shocked if much more than 100 GB or so were used by the OS and all programs you have installed.
I have a laptop, recently purchased, with a 2 TB HDD on to which I transferred everything I've been carrying with me for years from another machine, including a large Music library and Photos library, and I'm just under 500 GB in total.
My Program Files and Program Files (x86) folders are 11.5 GB, Program Data is 16.6 GB, and Windows is 23 GB for Windows 10, Version 1803 Home. The grand total is right around 50 GB.
I used Folder Size to scan to get these figures.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
Memory is a crazy woman that hoards rags and throws away food.
~ Austin O'Malley