Dear Chris,
Its good to talk to you again. Ill go straight to your questions:
How much emphasis should you put on your personality traits when figuring out where you would fit best? I would rephrase the question (it makes a big difference when you do) and change the last part instead to the obvious, ...figuring out where God is calling you. Its not just a question of where we fit best. In seeking our vocation we are trying to see where God is calling us, we are trying to be as generous as possible with him, and we are offering ourselves to him.
Now some of our personality traits are learned and can be changed, while others are so ingrained that they can be considered structural to us and can only be modified up to a point. These structural elements are what let us know what God did (or, more easily, did not) make us for. If you dont think that you would be detached enough to be a good husband, just figure how detached you have to be to be a good priest. It is not an uncommon struggle, and detachment is absolutely necessary for our human maturity. Your lack of detachment is probably modifiable enough, with the help of grace certainly, to become a good husband. I would recommend you start working on it and see how far you progress, so as to discover if you are able to take the extra step in generosity that the priesthood entails. If it is beyond you even with the help of grace, then you dont have a call.
Can a vocation be destroyed? A vocation is a call and our part in it is to answer, say yes or not to it. Since we are free, we most certainly can make a mistake, or be ungenerous, or even rebellious; the outcome being that Gods call does not receive the answer he was looking for. In the case you mention of someone jumping around a lot, never settling in or seeing his decisions through, yes it could conceivably ruin a vocation. However, the problem is not simply the reputation he gets for himself, but more fundamentally and importantly a trait that he acquires, a virtue (consistency, stick-to-it-ive-ness) he has not formed or matured in himself. All the indecision, stepping back, etc. may be a product of your temperament as well as your education and upbringing, so you need consciously to start developing the virtue of perseverance and decision in order to enrich and form your character and personality.
Start by taking on some daily spiritual commitments - not too many, ones that you can handle - but the key is your resolution to fulfill them every day, and then your perseverance in actually doing so. It could be a Rosary, or ten minutes of Gospel reading, or daily Mass... but the key is going to be to stick at it. And as you make the effort, ask Jesus for the grace to put him at the center of your life. Then, simultaneously, you should take stock of your other duties, be they work or study, and tackle whatever inconsistency you discover there.
I hope that helps and encourages you a little.
Be sure of my prayers.