What kind of NAS is it?
The more containers you run, the more demand you put on the resources.
So I don't have a NAS or anything but it seems as though Synology offer you a way to integrate docker easily, see this guys blog
Open up the package center and find docker, there should only be one
Then you start running containers. The dude in the blog started with MySQL but you can start with a PiHole or Plex or something else you might need to run locally.
This guy has the same NAS as you do and asks a question about performance of Jenkins and Gitlab (which imo would never run adequately on such a small box)
I'd say start small by running 1-2 containers like the ones mentioned above and observe the impact on resources.
dual core with 2gb of ram is gonna be tight
I don't need to run a docker I am fine with Plex directly from plex.tv with the nas version synology package.
Though I still may try just for the heck of it.