Although it’s possible to follow Lemmy’s communities in Mastodon, I would not suggest it as the experience is not the same.
That’s my reason to have separate accounts.
If you only want to be “notified” of new posts in a given community, I think you can subscribe to some sort of RSS feed.
In Calckey (now Firefish), you can add timelines that will show specific RSSs.
Although it’s possible to follow Lemmy’s communities in Mastodon, I would not suggest it as the experience is not the same. That’s my reason to have separate accounts.
If you only want to be “notified” of new posts in a given community, I think you can subscribe to some sort of RSS feed. In Calckey (now Firefish), you can add timelines that will show specific RSSs.