Yeah, everyone has to find their own way of organising, I guess. For me, there are too many different little projects that it would get messy throwing them all in one folder. And they’re so varied that I couldn’t think of one single “theme” or topic for most of them. Nothing I would remember a week later anyways.
I’d suggest /opt/docker/_compose/ for all the compose files. Or, if you keep all the config files for your containers on your NAS, maybe create a share there and put all yml files in it, then mount it on the host. This way everything is on your NAS and nothing is lost if the host freaks out.
And I’d add the NFS mounts to the compose files as well. When specifying volumes, you can use anything the host OS has a mount.xxx command for. Docker will take care of mounting everything.