Hi. I'm afraid there is no tool to migrate from a Pleroma account right now.

Yes, writing a script to port your posts could be possible in theory, but each post has an id that is an URL and as far as I know Pleroma and snac URLs are very different, so it may not be worth the effort.

You cannot transfer the people that follows you; I'm told that Mastodon does this (somewhat) by redirecting from the old account to the new one, but as far as I know you must keep the old account alive. People complain all the time about the reliability of this. I sincerely think that the best way to move your followers is writing a post saying "this is my new account from now on; please follow me".

The only thing you can reliably transfer is the people you follow; snac includes a command-line option to follow an actor, so you just need to feed it a list of actor's ids and that's it. Mastodon includes a way of exporting the followers as a comma-separated values file, I don't know if Pleroma has a similar option.

I apologize if the lack of viable options is disappointing to you.