An answer of sorts
Very well said OsmundL - I wish more people would realize that a boat, a design, a specific rig will never be perfect - just do the best you can and actually do it!
"So, my question again is what characteristics do matter the most in their effect on seakindliness/seaworthiness of an offshore boat?"
stipakb I will try and answer your specific question repeated above....
The best description I ever heard that I would apply to a sailboat I was going to buy is: "She was moderate in every aspect." If you keep that in mind along with what OsmundL said you should be fine.