When is it honest thoughtfulness and when is it indulgent confusion?

I am 44 years old, married with 3 kids (7-9-11), I am the primary income earner in our family, and I am debating quitting my job and going back to law school. I have a good job, it pays well and gives me a lot of flexibility (I am an independent contractor and work from home) and overall is a nice job. But I have no passion for it. BTW – I write medical manuscripts and articles for doctors who don’t have time to write their own. I’ve been doing it for 12 years and while it has met my immediate needs, I want to do something I really care about. So now I am considering specializing in International Law so I can work on human rights issues. I am scared. I recognize that this discomfort is natural and means I am growing and evolving. But I also don’t want to be foolhardy. What if I destroy my comfortable lifestyle and end up in a job that takes over my entire world and eliminates all my time with my family? What if I get through school and then there are no jobs in Arizona, where I currently live, and my husband refuses to move? (My husband is a school teacher, and VERY adverse to change, and this is a very real possibility!) There are so many what if’s! How do I define what is a healthy amount of research/introspection and when I have allowed fear and discomfort to stop me from progressing?