Hi,
and welcome to the avast forum.
To start, I'd like to learn a bit more about your network. So, you have 137 different sites - which are not connected with each other? Or are connected over the Internet (VPN)? Are connected using private lines?
Also, how big are the sites? Do they have their own network admins?
Can you please also tell us how did you use Sophos in your scenario? Did you use the Enterprise Console? Were you generally happy with Sophos remote management capabilities (I'm not talking about virus detection)?
Thank you

Vlk