Dex is good, but IMO it's not as vital as Con. Sailors were dying a LOT, and it wasn't from accidents. Con would help a lot with diseases (those were rather common on sailing ships), the exhaustion inherent to working on a sailing ship and the lack of nutritious food. And scorbut, which is a disease, was one of the biggest issues in intercontinental sailing.

Darkvision might not do jack for navigation, but it would be very useful when you need to work day and night and the only available light sources are torches, oil lamps, candles, moonlight and starlight.

The OP never even mentioned pirates.

AFAIK most sailors couldn't swim at all, and when would the lower speed actually be an issue? In most cases, it's all about whether you get exhausted before you're at your destination.

Great point with the submarines, though.

The height being an issue for other creatures gave me a funny thought. If dwarves didn't build massive structures and instead built for their height, people invading them would have such an issue. You'd have dwarves running through halls chopping at them while they're crawling around or bent down. Invaders wouldn't stand a chance.

Dex is valuable for tall ships, but steamships and ironclads, str/con is the way to go.

For sure wisdom being the highest priority unless they always sail near the coast, but to be fair you only need 2 people with high wisdom

These are all problems humans already have and try to get around. A few adventurous and entrepreneurial dwarves is all it would take to kick start the golden age dwarven naval empire.

I am looking at this from a fun world building viewpoint and I find this idea exciting.