I am not sure about the details of intended behaviour but it certainly won't federate to anyone deliberately disabling that part of federation so for privacy purposes you might as well assume that it doesn't federate.

I’m not one to half-ass it, so someone more knowledgeable than me will have to field these.

I can't answer your question about the votes, but posts and comments are retained when you hit the delete button. The only way to delete them is to edit the content beforehand. I believe moderators are capable of restoring posts, but I haven't checked the comments yet.

There's no reason where this has to be the behavior by default; federation alone is a challenge but not an excuse. Ironically, when it comes to privacy, a company like Reddit (with sketchy privacy policies) might be better than Lemmy (a series of entities in a variety of jurisdictions where your data is protected by the weakest of all of their privacy policies)