Everything about this piece revolves around supporting (both literally and aesthetically) the live-edge top. We spent nearly two hours comparing several options at the hardwood supplier, deciding whether we wanted one wide slab or a bookmatched pair of boards that would net the required width. A good rule of thumb is that a dining table should be between 30"-36" wide and allow 24" along the long dimension per person. As this table will fit a small dining room we are opting for a slightly narrower width.
The customer fell in love with a slab that runs the full gamut of the black walnut colour palette - from blonde to gray, to purple, to deep brown. The inclusion of sapwood is a personal choice that I fully support since it adds to the dramatic nature of the top. This particular board has a large, stable knot in the center that not only creates a focal point, but generates a fair bit of figured grain.
There are many great tutorials on the web about how to flatten a top, so I won't go into too much detail here. My experience is that these single slabs have a predominate concave/convex side and there may be some rationale about which should face up. Our decision, however, was based entirely on appearance. This meant that the underside (where I start the planing process) was the convex side. I start with a scraper to remove any gunk, and plane at a 90 degree angle and toward the middle from each side with a 5 1/2 plane until I am taking shavings (more like fine splinters) from about 95% of the slab. It is then generally time to resharpen, set the the plane to a finer cut, and then plane with the grain. With the use of a straight-edge and a pair of winding sticks you can trust your eye to get it very close.