Cold face – not a lot you can do really. Neoprene balaclava to stop ice cream head but face ache is pretty inevitable.
Sea sickness – as you said bi-lateral breathing in the sea is more about breathing to the side where you won’t get a mouthful. I do tend to get a bit of motion sickness when swimming in a rough sea, but very mild. Cold water hitting the inner ear makes me dizzy and sick so I’d 2nd ear plugs, they make a huge difference especially in very cold water.
Depending how hard you are swimming, getting out is often a problem for me too with dizziness. Pretty sure the cold makes it worse.
Reading this back to myself I’m starting to wonder why the hell I bother!