98 altima stereo install

My girlfiend asked me to intall a stereo for her. i put mine in my tundra and it was easy enough, but haven't taken apart an altima yet. crutchfield say the car takes 6 3/4 speakers all the way around is this true? What about depth? Is there a window track behind the front speakers like on a Tundra? is the Depth limited?

In another thread it mentioned the airbag sensor being behind the headunit. Can it be set off accidentally?

Any tips are apreaciated before the project gets going.