This is clearer. But I still think you are leaving out most meaningful context, and approaching this in an upside-down way. Instead of starting with a higher-order goal and figuring out a workflow that makes sense, you fixate on this one idea as the only solution. All because of a set of self-imposed constraints that you dismiss any notion of reevaluating. It seems unproductive.
(Missing context: What type of work do you do? Under what circumstances? What kind of data are you working with, and roughly how much of it? Why does it all need to be in DEVONthink?)
I am reminded of this perceptive post:
PS: I don’t know much about WebDAV, but my impression from skimming discussions in the past is that it is actually possible to set up and rent WebDAV storage from an external provider, and that you don’t need your own NAS.