Thanks, this is a good start.
It sounds like what you really want is a shared network drive that's mapped to a directory on the NAS. If it's just for storage and performance isn't critical that would be a lot simpler than syncing a local directory across multiple systems.
For this one, it is just storage, but I won't always be within my WIFI range (so I'm thinking local is probably best), and really I've been keeping 1TB of downloads files on both machines all this time anyway, so it's not really an increase in my storage expectations.
Otherwise, you need to decide if you want the syncing to happen in real time like the Dropbox client does it, or if just syncing once a night at 3AM or something is good enough. If you want it to happen in real time then you need something which gets installed on both the NAS and each of your sync'd systems that monitors the disk, and manages sending files to and from the NAS when they're updated. I believe Synology offers applications which can do that; they call it "drive" or "cloud station" or something. I just do backups nightly with rsync so I haven't really looked into that.
Yes, Cloud Station is the old one..."Drive" is the new one. I've already set up and tested the replication using Drive. I actually like it a lot, plus it keeps logs of all files being changed, added, deleted, and the status of replicating those changes.
I'm thinking locally accessible partitions would be good here (particularly on the laptop) because I won't always be at home. And my use-case is pretty simple: Most of my download files are applicable to both machines anyway.
For example, if I download an ISO file on the workstation in support of a beta team that I'm on, I'm probably going to need to install it on the laptop too. Maybe not immediately, but probably "at some point soon". If I download a new version of Filezilla's installer on one machine, I'm going to eventually want to use it on the other. Probably 99% of what I do will be "the same thing for both computers."
For the laptop, synchronization does not need to occur while I'm on travel or otherwise not connected to my WIFI network. But I do need access to those files when I'm away from home, and I'd like to not be limited by transmission speeds or the possibility that my house has a power or internet outage and my NAS is down. So local + replication is the way, I think.
I understand the issues with deletions...that deletions on one of the devices will get replicated to the others, resulting in the replicant versions of those files also being deleted on all of the devices once replication resumes. I'm okay with that, because I need to reduce repetitiveness (me deleting, adding, changing files multiple times on multiple devices). Plus, I will be taking backups on a regular basis anyhow (I just need a workable strategy).
If this works okay with my download files, then I'll implement similar setups for my photos (I need to figure out how to combine my iCloud photos with those on my PCs), data documents (kind of like my own version of "Google Docs", videos, website source, and basically everything that I might need access to, regardless which device I'm on.