We use bedrock from Roots: https://roots.io/bedrock
/, it's a Dependency Manager that uses php composer to install and update plugins. Your plugins are premium so for now it's not posible to install the plugins via composer.
We install normal plugins via the https://wpackagist.org
Perhaps it is possible to look at this in the future. Thas it's also posible to install your plugins via composer, through a unique download url per account with a unique key/token.
Thanks for the time,