Linkwheel Keyword Question

I was reading lemonarian's linkwheel guide (the complet pdf one) and I had a question about the phrasing on the keywords.

"You target one keyword per linkwheel."

Does this mean the 7 sites in the linkwheel should be based on the one keyword or that each of the 7 sites should use a different keyword?

This then poses the question, what happens after the first level and I move on to sub-wheels. Can I use the same 7 keywords. 1 for each of the 7 parts of the sub-wheel or do I need to come up with yet another 7 keywords?

I realize I can really do whatever I want so "need" may not be the best word. What do I need to do to take best advantage of the time I'm spending doing this?

As a side note, if somebody really wanted to could they make a 20 site main wheel or would that be overkill and hurt the effectiveness of the wheel?

This thread might be helpful to you: http://www.blackhatworld.com/blackhat-seo/black-hat-seo/100159-unusual-linkwheel-effect.html

Thanks for the help. I think I know what I'm going to try now