The only guideline I'm familiar with is "Tell me three times - tell me what you're going to explain, then explain it, then tell me what you just explained." This seems to work on multiple scales - from complete books to shorter essays (though I'm not sure if it works on the level of individual paragraphs).

There's a general rule in writing that if you don't know how many items to put in a list, you use three. So if you're giving examples and you don't know how many to use, use three. Don't know if that helps, but it's the main heuristic I know that's actually concrete.

It really depends upon the topic and upon how much inferential difference there is between your ideas and the reader's understanding of the topic. Eliezer's earlier posts are easily understandable to someone with no prior experience in statistics, cognitive science, etc. because he uses a number of examples and metaphors to clearly illustrate his point. In fact, it might be helpful to use his posts as a metric to help answer your question. In general, though, it's probably best to repeat yourself by summarizing your point at both the beginning and end of your essay/post/whatever and by using several examples to illustrate whatever you are talking about, especially if writing for non-experts.