Depends on your license. Example our license is E3 Office 365 and I interpret that you get number of API per user but also get any unuse API by other users. Example we have 2000 E3 but only a handful of users. So if it is 2000 API per day, then it would be a total of 2000 * 2000.
And also what happen if i exceed the API for today?
How does it charge?
What happens if any user exceeds Request capacity?
If any user exceeds request capacity, admin for the tenant/environment would be notified and would be able to assign Power Apps and Power Automate request capacity to that user.
End users will not be blocked from using the app for occasional and reasonable overages at this point of time.
Will my Integrations stop working if application users exceeds Base Request capacity?
Integrations will not be stopped for occasional and reasonable overages at this point of time. Administrators would be notified about overages and will be able to add Power Apps and Power Automate request capacity to be compliant.
Note specifically "reasonable overages" - you may be allowed to go slightly over, but don't push it too far.
Also for your other question the below maybe useful, also from same document:
For these users, every tenant will get base request capacity per tenant which can only be used by these users and not by users with standard licenses.
This base request capacity would be based on the type of subscription and would be as follows:
If a tenant has at least one Dynamics 365 enterprise subscription, they will get 100,000 requests per 24 hours
If a tenant has at least one Dynamics 365 professional subscription, they will get 50,000 requests per 24 hours
If a tenant has at least one Microsoft Power Apps or Power Automate subscription, they will get 25,000 requests per 24 hours.
If a tenant has multiple type of subscriptions, their base request capacity would be max of two subscriptions. For example, if a customer has both Dynamics 365 Customer Service and Power Apps per user subscription, their base request capacity would be 100,000 Requests per 24 hours.
Also, note this:
Do the Power Platform Requests entitlements roll over from day to day or month to month?
No. All the power platform request entitlements are calculated on a rolling 24-hour period. If they are not consumed, they don’t roll over to the next day or next month.