The file download size for the Core Launcher is ~2.5GB. Once installed, the Launcher requires ~5GB of disk space.
To check the total disk space left on your Windows 10 device:
1) Select File Explorer icon from the taskbar or the home button
2) Click on PC on the left.
3) The available space on your drive will appear under Devices and drives:

We recommend always creating a backup of your projects in case your main drive gets compromised/corrupted. You may do so by simply copying the CORE folder to another storage device (a USB Drive, Google Drive, etc).
Once you confirm the amount of space you have on your device you are ready to download and play Core for free!