Speaking as someone with a small channel who hasn't done live events on YT before but has with other services, I think it helps a lot to schedule them. I've done on-the-spot livestreams before (off YT) and they don't get as much attention compared to those that are announced ahead of time. I think for smaller channels, that's a better way to start off if you want to do livestreams in terms of getting the most people possible to view them.
As for when, in general, to start doing livestreams, maybe ask your subscribers if they're even interested in the idea? I guess it all depends on the person, if you get 1-5 people really interested in it, would that be worth it for you?