I'm not entirely sure any of that would be effective in controlling visibility of spam accounts from other instances. I'm quite sure that up/down voting does not always federate perfectly. Those steps would all be effective in handling malicious accounts on the same instance they're registered with, as long as their malicious posts and comments are also on that same instance; the effectiveness would certainly fall off sharply for content posted at other instances.
I wonder if there needs to be some kind of "governance board," like the NATO or EU of the fediverse, where major instance admins meet and set agreed upon standards of instance behavior.