~20 GB for the full offline ISO. Not practical for slow or metered connections. Also requires a large USB drive (32 GB+ recommended).
While rare, the automated detection can sometimes install a generic driver that performs worse than the manufacturer’s specific one. Graphics drivers, in particular, may be suboptimal. --- Driverpack Solution Windows 7 Offline Download
The entire driver database is stored locally. You can install network, storage, USB, and other critical drivers without ever connecting to the internet. ~20 GB for the full offline ISO