Hmm I’m not sure if it affects local.

Because they’re basically the same as a post or comment, it’s how the fediverse works. They get sent out to anyone listening, and whoever is listening directs it where to go i.e. a community or users inbox. So all instances can update with a new post to their users who are subbed. In theory the DM would get ignored by everyone else who isn’t the target, but one could easily set it up to not do so.

Yes.

I don’t know of any clients that publicly show it, but the information is sent out as a json that can be read by anyone setup to receive them.

The Fediverse is open, everything you do on here is fully public.

It’s why I prefer it over reddit, where who knows what really happens with all the vote manipulation and brigading.

To answer your question, it is all listed alongside upvotes on the posts if using mbin.