Just on the sink cutout-well, of course it does. But so what?

Promise me that you and your descendants will not tap dance in the sink. That should take care of the weakened issue.

Promise that your husband won't try to clean an engine block in the sink.

Seal the BB with something like poly on the bottom and around the sink cutout.

We are in the process of doing the same thing. There is so little information out there on these things, but I did find this site while researching and it gives pretty good instructions for installing wood countertops. They address the dishwasher and stove issues.

http://devoswoodworking.com/Installation.htm

We are going to use pure tung oil to finish ours. Food safe and non toxic and water proof. Just make sure it is pure and not from the big box stores if you use this. Boat builders used it for centuries and if it waterproofed boats, then it ought to handle what water there is in a kitchen!

We put Waterlox on our IKEA butcher block counters. Also, IKEA recommended installing their FIXA diffusion barrier (a narrow strip of something like plastic sheeting) on the underside of the counter over the dishwasher. This was supposed to be additional protection against moisture/steam from the dishwasher. It cost, I think, maybe $3 if you're near an IKEA. Or I'm sure there are similar products elsewhere.