Hi,
generally there are no restrictions on number of users or devices that can use a single API key but we do recommend to use dedicated API keys for separate code bases, e.g. if you're building an iphone app, android app and a web site we'd suggest to use 3 separate API keys.
But for full-length streaming services this might vary depending on your licenses with content owners (i.e. music labels) and their requirements for your specific use case. Please note that we can provide access to streaming functionality only if you hold these licenses.
Thanks
Filip
7digital