How private are separate Android users? My new job uses Workplace by Facebook, and Workplace Chat is their preferred messaging platform.
However, Facebook's apps asks for about every possible permission (see below), which is why I don't use them on my phone.

If I create a separate user on my Android phone, and install Workplace to this "work" account, preventing this user from making calls and sending SMS, will the Workplace app be able to "spy" (calls, microphone, networks, etc.) on my main account?
If I create a separate user on my Android phone, and install Workplace to this "work" account, preventing this user from making calls and sending SMS, will the Workplace app be able to "spy" (calls, microphone, networks, etc.) on my main account?


No.

App developers must handle supporting multiple users and are offered hooks through the UserManager API to do so.

The only way an app can interact across users is by specifying the signature level permissions 

INTERACT_ACROSS_USERS (signature|system)
INTERACT_ACROSS_USERS_FULL (signature)


These permissions require that the app be signed with the same key as the system.

So, Workplace cannot access data across different users.