As to splitting the attributes, I'm not sure there's a magic to it. But here's why I'd go more heavily Dex.
Depending on your class, increasing certain attributes increases skill damage (for Vixen, it's Dex). So that's why I'd do only 157 str for the str items, then the rest on Dex for skill damage and crit increase, etc. I don't know why you'd ever do Int at all unless you were using Int items. Even then I don't know why you'd use Int items unless it's for weapon procs. Really I think your options are pure Dex (Weaker) and Dex/Str (Tougher).

I think you should just look over each skill and what it does. Like I said, the only skill I think you should completely ignore is Bandage, since it is next to useless because it turns off in combat.