Hello, We used a slab of reclaimed old growth cedar as a unique countertop with a hand blown glass sink in one of our offices: We paid about $500 for this slab. In our master bath, we have two Wm. Garvey teak wood vessels. These are incredible sinks and look the same today as when we installed them 4 years ago. Just soap and water clean up and some teak oil about once a year. I've put a link to the website where we bought them. Good luck! Here is a link that might be useful: Wood Sinks

Those are beautiful cabinets. They really call out to me for something in a walnut tone, like the link below. Or at least that general caramel-y color. (You might find some teak like that.) The other option might be to try to minimize grain since the counters have a pattern, in which case maybe you'd like something in a very ungrainy stained maple cappuccino type shade. Here is a link that might be useful: Walnut floor

For me that would primarily involve a jointer and surface planer to dimension the individual sticks, a bunch of heavy clamps long enough to span the whole width during glue ups, my finely tuned hand planes to level the surface and my sliding table saw to cut the ends off square after the last glue-up. An industrial manufacturer would have oversize/automated versions of similar equipment, except their hand plane would be a wide-belt sander. Oh, and a router to shape the corners. Methods of work vary, though; if your guy is a competent woodworker you shouldn't get too hung up on the specific tools. I'd hate for you to dismiss your guy's ability to handle the job because I, whose work you haven't seen, said you need sash clamps and you didn't know that the pipe clamps he turns out to have are functionally equivalent. If he knows what he's doing he should be able to tell you whether he's equipped for the job. If he's not sure himself, and is planning to wing this project, then he should be the one asking questions.

The top surface of the counter appears to be drying faster than the bottom, so it is shrinking, and that causes the warp. This suggests the wood maybe was not fully dry/stable, OR as suggested above, that layer at the bottom may have played a role. One more thing that has not been mentioned: is there a finish on the bottom to match the top? It should have been varnished to equalize the movement of moisture in and out of both sides of the wood. The crack probably happened, again, because of drying shrinkage, AND the wood was not allowed to 'move' horizontally. If it was secured fastened down across the width of the counter and didn't have any play in the fastening system, that's when it cracks. Wood has a characteristic amount of shrink/expand across the grain and along it, and it varies by species. Plywood is very stable because the grain alternates directions in each layer. Solid wood is more difficult to deal with. This kind of counter top CAN be done and often is. It may need some rethinking and redoing. I built a 36"x48" island 20 years ago with 2" thick solid black walnut and hickory, alternating, each board about 8" wide. It was air-dried lumber I harvested myself. It did cup just a tad after installation but it's been stable ever since.