Is formatting the disk sufficient, or do I also need to flash the BIOS?
If a BIOS flash is necessary, where can I download the full BIOS firmware?
I found some BIOS updates here, but they seem to be incremental updates rather than a complete BIOS image, am I correct?
Any guidance would be greatly appreciated. Thank you!

Hello pirr,

Welcome to Lenovo Community

I understand that you are concerned with bugs and malware on your second hand ThinkPad T480.
When purchasing a used laptop, it's a good practice to ensure that the system is secure and free from any potential malware. Here are the steps you can take:
-Formatting the Disk: This is a good first step to remove any malware that might be present on the storage drive. Ensure you perform a full format rather than a quick format to thoroughly clean the drive.
-reload the BIOS default settings, be sure to save
-install all applicable updates offered in the support site
-install all OS updates
Hope this helps.

Best regards,
Lorenzo_Lenovo

If you have need or are interested Lenovo is currently running a surplus parts sale in North America, EMEA and Asia Pacific regions, a lot of parts are offered at heavily discounted prices.
Visit the Lenovo Parts Clearance site to see the offerings.