Yes, you can use an external hard disk during the Windows 10 installation process.
Yes, you can use an external hard disk during the Windows 10 installation process.
Avoid modifying your laptop if it's covered by warranty. I advise against altering internal components since previous issues have been problematic. Consider swapping the HDD for an SSD and performing a fresh installation.
You only have a 250GB SSD, which isn’t enough. You also need an additional 1TB HDD.