By far it is easier to upgrade rather than migrate from one ePO to another new ePO (new Database) with MDE installed. MDE did not support migration from one server to another until MDE 7.1.3 and all clients must be running 7.1.3 in order for the functionality to work.
Currenlty no version of ePO supports Server 2016. For the list of supported OS's, please review KB51569.
If you wish to migrate to a new server, you can follow the guidance in KB66616 which will allow you to move to a new server while maintaining the current database. If this is a 32 bit server (Which isn't supported with ePO 5.1) additional steps need to be taken to migrate from 32 bit to 64 bit (KB82808).
Before you upgrade, I would reccomending reviewing the ePO Upgrade checklist in KB71825.
Edit: You cannot export and import encryption keys. While a tool exists here on planet to do a bulk export, there is no supported method to import them. Systems will automatically upload the keys after they are transferred but this assumes the transfer is successful. Unless there is a business justification such as the company is splitting divisions apart or something along those lines, under typical situations, I have never nor will I ever recommend spinning up a new ePO to facilitate an upgrade.