I have installed Avast Internet Security on my Windows 7 machine but intend to do a fresh install of Windows 10 soon. Can I reinstall Avast on the Windows 10 system using all the same software credentials? Are there any other concerns I should consider?
Yep, should work.
If you have special settings in Avast, you might want to save them to a usb drive so you can restore those settings
once you re-install Avast.