(1.) Complete Vanilla, any plugins added will never interfere with gameplay. (Except for voting, which will be removed in the future.)
(2.) The server administrator will download your base (only if the base is large and significant) and will add it to a render queue, they will eventually be added to the servers website archive.
(3.) The server administrator will never interfere with normal gameplay, only if one player is attempting to disrupt the performance of the server.