Aloha Marc,
Do you have the Diamond Edition? If so, the time feng shui of your specific house may have something to say about where to best place an aquarium.
Other wise, look at the chart on page 13 in your Level One manual. The directions you've listed have water as it's principle element (as in the case of North), or that it's principle element is enhanced by (as in the East).
When you decide where you are going to place it, then consider balance. A tank size that balances well in a big living room may not balance well in a small one. As for color of gravel, et. al., look to support the element of the area you are placing it in.
Much Love, Shawn