Regarding Always On Licensing (Secondary replica no license required)
"Readable Secondary" AG setting for all the replicas associated to
  Always On(including current Primary replica) should have setting
  either as “NO” or “Read-Intent Only” or it should be "NO" only?
  There should not be any Standalone Database? (not even any third party
  backup tool database such as "LiteSpeedLocal").
  Also the backup should not be configured to run on Secondary replica. Otherwise, the Secondary replica will not be truly passive. Is it true?
  



Must be set to "No" so that it is not readable. From the licensing data sheet:



  The secondary replica used for failover support does not need to be
  separately licensed for SQL Server as long as it is set to ‘not
  readable’. If it is readable or serving data, such as reports to
  clients running active SQL Server workloads, or performing any “work”
  such as additional backups from secondary servers, then it must be
  separately licensed for SQL Server.



A standalone database doesn't violate the passive license unless it is used for something, anything. No backups, no queries, no integrity checks, index or statistics maintenance. All of it would constitute production use and violate the terms. Easier to not have any standalone databases.
If you run backups against the secondary it will violate the passive licence terms and require a paid licence.


Further information can be found in the licensing guide and licensing data sheet. Note that this information is for SQL Server 2017. It hasn't varied too much since 2012, but best to validate with your specific version and run any concerns past your licensing reseller for official confirmation.