A big following sea and losing rudder control is more of a concern IMHO. Storm windows and/or thicker glass can alleviate the points you bring up.
"An N60 can do a 2000nm crossing @ 9kts with 20% fuel reserve."
GREAT! about 1/2 of the range may be required on a Pacific adventure.
Yes, those Aussies are a clever lot....There`s a surprise, Seabrake, an Australian designed product. The manufacturer, Burke, was started by Martin Burke,originally a sail maker, who made and repaired sails for my sturdy Folkboat, and has added a range of marine products, like clothing, bags, safety gear, etc.
My (louvered) engine vents are on the pilothouse sides. I suppose a thin, bottomless "boxes" could be installed to reduce possible water entering during heavy seas.
engine vents , we put them on the side of the cabin , and inside they have a "chicane" like you can see here
http://long-cours.62.over-blog.com/photo-1911172-prises-d-air-001_jpg.html
but for the next one we will put them on the center line they could be floaded llittle later .
Actualy it is little before 90° heel
It is less than our Avs
Get a copy of "Voyaging Under Power", hopefully a first edition and it will tell you most of what you want to know. I read mine maybe 3-4 times, and use it as a reference book.