Choose a neck first. That'll sorta drive your body choice, appearance-wise. Sound-wise, the body isn't terribly important. It's a mounting fixture for your pickups, neck and bridge as well as a string anchor. On the list of things that influence an electric guitar's tonal character, the body is down the list a way.
I'm not sure what "chewy mid frequencies but not too dark on the low but dark enough" means, but I suspect an Ebony over Wenge neck would give you something like that. If nothing else, it would be a joy to play. Wenge has a unique feel to it that most people fall in love with. Also, no matter what else, put stainless frets on it. Trust me on this one; you won't be sorry.
If you like the look of Koa, you may want to consider putting a Koa top on a piece of chambered Alder or Swamp Ash. Koa is heavy stuff, so even chambered you probably don't want a whole body made of it. Doesn't get you anything for the money other than lower back and shoulder pain.