Newbie Needs Help With Milage!

I am a new Homecare RN, and I do visits daily - and I track my milage by the odometer...however there has been great debate on a few issues. If anyone could shed some light I'd appriciate it. ..

1. If I occasionally use my other vehicle - do I need to track that separately?
2. I heard that the IRS requires that you have atleast $10,700 in deductions to claim milage. Is this true - I've been on the IRS.gov site and can not find any thing to specifically answer this question. I currently do not own my home so I know I don't have that many deductions.
3. Do I need to track this by odometer milage or can I just write my milage for the day. Some of our nurses just write thier milage in thier day planner for the day and add it up at the end of the year....What's a newbie to do!

After hearing the $10,700 thing I started to panic because I'm traveling almost 200 miles a week, sometimes more! I will be bummed if I can't claim that!!!