How many main points or ideas should each paragraph in your paper contain?

 I would give it one point per paragraph. A paragraph should contain a complete line of thought. Thus if you need to use several sentences to support a single point (or thought) then that makes the paragraph.

I had been taught that if one can complete a whole line of thought in a single sentence, then one should try wrapping it up into another thought (abstracting it), so you don't end up with a single sentence paragraph. But I've since seen many such paragraphs.

An effective way to ensure good paragraph structure is to go back and create an outline of your paper after you are done; with the subject of each paragraph being a single entry in the outline. If you can easily create the outline without confusion, then your paragraphs are clearly written.

In this manner, an argument might require multiple paragraphs before it is exhausted. If you have three points to make in an argument, it might be best to have three paragraphs. Two arguments with 3 points each would make up 6 paragraphs, and so on.