The best wood now is engineered wood. Although it might be nice to make one of all walnut, the results will be a table that needs a lot of work and leveling on a regular basis unless you have a humidity and temperature controlled environment similar to a test lab. Engineered woods expand and contract more evenly making the stability much higher. The thicker the slate the less vibration you have and consequently a more stable table in the long run. Building a table out of Steel and engineered woods like Soren Sogaard billiard tables and Diamond tables and keep the decorative woods just for veneers and non structural I think is your best bet. Good luck in your project.