I also use Obsidian for project and file management. One thing I’ve adopted is a convention of reserving the first digit of a folder’s two-digit prefix for the storage location:
0 = Obsidian
1 = File folder (on hard drive and iCloud-synced)
2 = Task-management (OmniFocus, in my case)
3 = Email folder
4 = DEVONthink databases
5 = Folder on One-Drive (typically shared with co-workers)
6 = Folder on SurfDrive (a research cloud service in the Netherlands)
I’m an academic, so have folders for Research writing projects (1), Teaching and supervision (2), University governance (3), Research project collaborations (4), Service to the profession outside my university (5), Personal (6), and Systems maintenance (7).
So, any folder in Obsidian about teaching starts with 02 (e.g., “02 Digital Ethics 2022-23”, whereas the OmniFocus project a project starts with 22 (e.g., “22 Grade midterms for Digital Ethics”)
For me, what is useful about this, is that if I’m running a search for folders, I can see right away whether something is a folder in my Obsidian vault (“02 Digital Ethics”) or on my hard drive (“12 Digital Ethics”).
I’ve not really decided yet whether to designate which of those folders are part of parent folders P.A.R.A., but I could easily do that. I toyed around with indicated that in the folder name (e.g., 12P for “teaching PROJECT on my hard drive”), but that got a bit fiddly. And there seemed to be a huge proliferation of folders. But I see the advantages of having just four P.A.R.A. parent-folders at the top level and then a small set of folders in an “ACTIVE Projects” folder and also a place (Archive) where projects and areas of responsibility go to R.I.P.