I agree that acceptance and belief (though not necessarily religious) are very important, but to me they are not choices. I didn't wake up one morning and say "Hey, I think I'll accept myself today. And I'll become an atheist while I'm at it." These things happen naturally as your experiences shape the way you view yourself and the rest of the world.
As for a partner, people who can't get by in life without a significant other seriously need to obtain some self-respect. Yes, it's lovely to be in a relationship, but life is no more difficult without one. I agree with you Kevin, that it's not all that hard to change professions, but it's harder to do that than to change the others, I think.
All in all, there is no one decision/event/thing that shapes who we are. All of the listed 'choices' contribute in some way to the person that we are, and to label a single one as 'the most important' would be overly simplistic.
Menzo