A disadvantage of your method is that the original dropbox sync is disabled before DEVONThink’ s dropbox sync works. This means that if something goes wrong with setting up DEVONThink’s sync your databases do not sync anymore. For that reason, I would in step 1 create a new DT database folder in the Documents folder and copy the database from the Dropbox folder to that folder (on relevant computers) and remove the original databases from Dropbox only after the DevonThink sync works fine.
Furthermore, it is my experience that databases on Dropbox get easily corrupted. For that reason I recommend that:
(1) clean up your database before you copy it out of dropbox on your first computer (or, better but more work, after clean up the copies after copying on all your computers) by opening the database package in the Finder (control-click on the database and choose ‘show package content’) and removing all the .dtMeta files that have ‘conflicted copy’ in their name).
(2) before you sync the database for the first time do a ‘verify and repair’ followed by ‘back up and optimize’ (both are in the tools menu) (this should be done on each computer, before the first sync on that computer)
See also this comment in another thread [url]Syncing and database location/storage]
Hope this helps!