How to migrate a multi-instance LSB script to systemd?

I wrote an LSB init script that can manage multiple instances of my daemon: rcfoo start starts all the instances (which are found in some /etc configuration file), rcfoo stop stops all the instances, rcfoo status displays the status of all instances, and rcfoo reload reloads updates the daemon with a changed configuration. First I wonder how to detect the instances to work on with some foo@.service systemd unit file. AFAIK I must specify all the instances like foo@A, foo@B, and so on. Second my LSB script can report an extended status, meaning it can display whether a service reload is needed (and my reload actually optimizes to only reload the services that need it). How can I make a custom status report? I think a script has to use systemd-notify for custom status messages. Fortunately my final extension to the LSB script, namely manipulating single instances by adding single (like in rcfoo start single A), is supported out-of-the-box with systemd. So my basic question is the first one.