As of now the Enterprise account allows us to create only one Sandbox account.
We are deveoping an application (Private App) to push data from a custom CRM application to Hubspot. We normally have multiple environments such as DEV, TEST and UAT before deploying the changes to Production. Ideally we would like to have corresponding Sandbox accounts as well so that integration can be tested in each of the environments (in isolation) without impacting other environments.