First question -- BlueSky is by invitation only and, no, I can't invite you yet. I haven't been on the platform long enough to invite anyone, but if you were looking for #MassSpecTwitter and for the coolest papers, Mastodon and BlueSky have them.
I need to figure out how to get into Mastodon again and see how it has evolved, but I might already be following more scientists on BlueSky than I ever did on Twitter.
I did put one post on Twitter this week so I could amplify a student's 63 page paper (!!) he submitted and posted on Biorxiv since Altmetric tracks Tweets but does not yet track reposts on BlueSky, but with bioRxiv joining the party, it's only a matter of time.