Big data Usage on "mobile documents" on new Mac as well as iOS

1 how can I verify that all files of the databases are synced and locally available on a given device?

You could look at the file counts in the Info popup of a database in DEVONthink To Go and File > Database Properties for the same database in DEVONthink.

2 if that has been achieved, Should I use the backup dialogue or something else to save a complete backup of the databases to hide away somewhere?

What backup dialogue ?

If you have proper primary backups running, e.g., Time Machine, the databases (and your other data) should be backed up.
Please refer to the Help > Documenation > Gettings Started > A Word About Backups for more information.

3 can I the somehow purge all icloud data created by devonthink?

Regarding the removal of iCloud Legacy sync data, I responded to this a week ago:

Here are the instructions again (and some additions)

  1. On the Mac, go into System Preferences > Apple ID > iCloud and click the Manage button. Select DEVONthink To Go then click the Delete documents and data button.
    This preference doesn’t give a realtime view of the deletion process, so close and return to the Manage section occasionally to check the process. Once iCloud has removed the data from Apple’s server, the DEVONthink To Go entry will disappear.
  2. Then hold the Option key, control-click the iCloud sync location and choose Verify Location Thoroughly. The results will be shown in Window > Log.
    1. In DEVONthink’s Preferences > Sync, right-click the iCloud sync location and choose Clean Location. This will clear out any sync data.
  3. After the clean is reported successfully in Log window or popover, disable the iCloud (Legacy) sync location.

4 lastly, I would then like to redistribute the database backup files to all Macs and be set from there plus simply re enabling / newly enabling icloud sync and wait until all is uploded?

Do you need to use a remote sync option like iCloud?
See this forum post:

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