Given your experience building boats, with carpentry, and with fiberglass, you should have few problems building a kayak for any purpose.

Attempting to cross an ocean in a kayak is not a rational decision. It's been done, I understand, a few times. One of the pioneers at this, possibly Lindemann?, was lost in a storm at sea after reaching one of the island south of Florida.

Any heavily build commercial boat should be capable of making such a journey. Ed Gillette made the crossing to Hawaii in a commercial fiberglass double. A home-built boat could also be made adequately strong for such a journey.

But here's the rub. Who knows how strong such a boat needs to be? The experience pool here is very small. I suspect that the paddler is a far greater issue than the boat in journeys of this type.