I agree with JD, your counters will swell and the joints will widen. I would consider using this temporarily, as a test if you will. If you find your using this kitchen a lot invest in a more durable,substantial surface. I would not put a lot of time and money using these tops.
I would not use any sealant as it may migrate into your dinner somehow.
Let me know when the steaks are done, i like mine meduim rare