What is the easiest or correct way of going from 16.04 on the old server and migrate to a new server running 20.04? 1. Upgrade the old 16.04 to 20.04 and then migrate? 2. Install the new server with 16.04, migrate and then upgrade the new server to 20.04? 3. Other way? (Even though I'm on a shoe string budget I could consider to purchase the migrate tool.)
Install the new server with 20.04, set it up according to the Perfect Server tutorial, and then migrate using the migration tool: https://www.ispconfig.org/add-ons/ispconfig-migration-tool/ I would advice you to wait for the release of 3.2 (currently in beta), because that will support Ubuntu 20.04.
Migrating is not necessary as updating the OS, the softwares and lastly ISPConfig will do as the easiest route BUT it is advisable to wait for the stable version of ISPConfig 3.2.
ETA for ispconfig 3.2? The release date is? I think next version the 3.1.16 is have ubuntu 20.04 support. Br. JaMBy