Please be advised that if you use the connect app, it doesn't always correctly parse links to lemmy posts. If they're not working for you, you can follow the whole plotline on my site. (These comics are in reverse chronological order, so start at the end and work backwards.)
There's some syntax that'd let you post to lemmy from mastodon, but I haven't found a way to get community content out of lemmy and into my mastodon, so... I'm still using the lemmy web client to make lemmy posts.
* Following a Lemmy community will add that community's posts and replies to your Mastodon feed.
* Replying to a Lemmy community post or reply comment from Mastodon will generate a corresponding Lemmy reply comment.
* (if I'm not mistaken) Making a non-reply Mastodon post that contains the handle of a Lemmy communtiy will make a Lemmy post within the associated community.
I'm open to being corrected about any of the above.
That was my understanding too, however, I followed RPGMemes with my mastodon account. While the client lets me follow the community, it doesn't import any of the posts to my feed, it just does nothing...
I guess the reason I wanted it is that I also maintain a couple mastodon accounts (including an account for artwork on the mastodon art server) - so being able to use one interface for everything would be nice...
I don't mind just having multiple tabs open though...