How many users and objects can be in an Oracle Database?
All Oracle Documentation can be found on-line
https://docs.oracle.com/en/database/oracle/oracle-database/index.html
It is highly recommended that you read the &quot;Concepts Guide&quot;.  If you understand just a tiny bit, it will make you a much better developer/DBA.
For your specific answer, you need to look in the &quot;Database Reference&quot; manual section &quot;Database Logical Limits&quot;.

Users and Roles  |  maximum   |   2,147,483,638
Tables | maximum per database | unlimited

App Design Notes
Web Users are normally stored in a table.
In Oracle :  Users and Schemas are almost synonymous.  This makes the requirement &quot;create an Oracle user for each and every Web User&quot; a very expensive task.... And a dangerous one at that.  (The last thing you want is L33TH4CKR to have his/her own account on your database)