How does lemmy differ from reddit?

Here are some specific questions.

• Are the upvotes and downvotes I make, private? If I report a comment, is my report private?
• Can someone follow me across lemmy instances based on my username?
• If I want to make a community, is there a reason I would choose one lemmy over another?
• Are the powers of moderators similar to reddit's?
• Where can I find a list of most active lemmy instances?
• Any other differences from reddit I should know about?