Can the site administrators determine from things like users’ IP addresses whether the same person submitted questions A and B, or whether someone is posting questions and answers to themselves?

Maezawa here. Actually, it’s not just IP addresses—we can see various other things too… *gulp*… That said, there’s no tool available for users to check this themselves, so you’d have to ask an internal administrator. When someone’s writing style seems similar, or when it feels like multiple posts might be from the same person, I’ve sometimes asked and been able to confirm that they were indeed the same person. (笑) Still, even if we know, whether we answer or not is determined by the content of the question, so I don’t think you need to worry about it too much.