Installing SQL Server TDE on a Windows Cluster
Several versions of SQL Server do not let you upgrade a Standard CLUSTERED installation of SQL Server to Enterprise.  Are you sure you can do this in your environment?  To clarify: If you are already clustered, upgrading to enterprise is not supported in many scenarios.  Secondly, TDE is a enterprise edition option.  You're not going to get to failover and test it without being on enterprise, but maybe 2016 enabled it for STD edition, I haven't heard of that though.  Have you tested this solution yet with your team?  

At the bottom of the MS supported upgrade scenario's it reads in the :

Supported Version and Edition Upgrades

"** Changing the edition of a SQL Server 2016 failover cluster is limited. The following scenarios are not supported for SQL Server 2016 failover clusters:
SQL Server 2016 Enterprise to SQL Server 2016 Developer, Standard, or Enterprise Evaluation.
SQL Server 2016 Developer to SQL Server 2016 Standard or Enterprise Evaluation.
SQL Server 2016 Standard to SQL Server 2016 Enterprise Evaluation.
SQL Server 2016 Enterprise Evaluation to SQL Server 2016 Standard."


The documentation makes it look like you can until you get to the end and read that tiny snippet.  

As far as TDE goes, it depends on how you do it.  In my implementation, the master key is encrypted by the Windows DPAPl (I think that's the right acryonym) service, but then the generated key is in the Master DB that gets moved between nodes as you stated on the database instance level.