"Next I past the whole post into a Mastodon compose field. Working by trial and error, I cut it down to <500 characters, breaking at a para-break and putting the rest on my clipboard. I post, reply, and add the next item in the thread until it's all done."
That's how I still do it, too.
However, IMO there are better ways to do this automatically.
If MS-Excel had bigger (rather unlimited) field lengths, I could program it myself...
pluralistic