Hello and congrats on your interview! I am in my first year of my MSW program and am a CalSWEC recipient.
To answer your questions:
My interview for the stipend was really straight forward, highlight your strengths, what skills you bring, and show your enthusiasm for your chosen profession. As for working for "the county," it really varies depending on the county you'll be interning at. Some counties have better reputations than others, and I have had a very fulfilling experience in Orange County (which is said to be one of the best.) With that said, there is more than one kind of field placement within a county, and you can experience a range of positions. Your experience will also depend on your field instructor and the amount of support you receive from your placement. There are so many factors that go into working for the county that it really depends.
The stipend is a financial godsend if you are attending a state school. After tuition, you will still have money left over. If you are attending a private school, that might be a different story. I believe the award amount is around $18,500 annually.
The two year commitment is a long time, but it's time that you will be learning valuable skills and honing your expertise. I also plan to get my licensure, and from what I was told by my field instructor, all of the hours accrued working for the county will be able to go towards your LCSW.
Hope that helped, and if you have any more questions, just ask!