What are the pros and cons of a used 2009 Nissan Maxima?

I am 22 years old and looking to buy a new vehicle in the next year. I currently drive a 2 door coupe and am ready for something more functionable and professional. I love the look of the Nissan Maxima. I was originally looking at the 2010 but couldn't find many differences between that and the 09. So if someone could pinpoint some differences, that would be great!
Here are additonal things I'de be interested in knowing:
1. Is 19city/26 highway considered good gas mileage?
2. What is the safety rating and number of airbags on the vehicle? I want this to be a vehicle I can grow into with 2 kids.
3. What should be the maximum mileage if purchasing used?
4. Is it smarter to buy used than new?
5. Since I am not looking to get this until the next 6-8 months and at most a year...how much should the price drop from now. The models I've been looking into (white 2009 or 2010 Nissan maxima with sunroof, tan leather interior, wood paneling, premium sport package) have been around the $24,000-$27,000 price range and I'm looking to spend $20,000. Should it drop/be negotiable to that rate or lower?

Thanks!
Any additonal information would be wonderful!

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