Moving Roon database to SSD

You are mixing this up with exFat. I don’t recommend using exFat for the volume that holds the database. On a reboot of your Diskstation the exFat driver will load after RoonServer has started and RoonServer needs to manually be launched again.
Ext4 is the common and native filesystem of Linux system (and also of your Diskstation). It can be selected when you format a drive in the “external devices” section and does not need to be paid for.

RoonServer will check its database location on every start of the app. When you stop RoonServer and rename your “RoonServer” folder to something else, it will be ignored and won’t be used anymore. So you don’t need to delete it and can keep it for the migration process under a different name. When you create a new shared folder or rename an USB volume to “RoonServer” it will directly be used when you start RoonServer again.

The RoonServer app itself can only be installed on internal bays of the Diskstation due to the architecture of the Synology operating system. So there is no need to reinstall the app.