I Believe the device limit is 1,000 or around that limit. For larger installs you would need to use the Avast Enterprise Admin Console.
Also, it is completely free, yes even business use. However it does have limitations, such as no MSI package for deployment and it does not run on servers, unless you pay for the premium version. You can purchase the premium version directly from the interface, or through a local reseller (reseller may have special pricing for you)