I think this might have been covered but using a hand held meter gives you many advantages.

It is an incident meter, it is measuring the light falling on the subject not reflecting off of it. I find it to be 100% accurate.

If you are using flash outside as a fill or mainlight you can meter the amount of light hitting the subject with great accuracy. (you need a flash meter version). I have learned to trust my meter more than the preview on the back of the camera.

I very seldom use my in camera reflected light meter. It is designed to analyze an average seen. Try that on snow or a dark background. The hand held meter will be accurate in both situations.

The best way to get everyone in focus is to be the same distance from the front row as you are the backrow. The easiest way to do this is by elevating your position. This will also work for your lighting, if your lights are higher the difference in distance is minimized so you don't have light fall off. (Inverse Square law) It will also help head size, so the front row head sizes are not way bigger then the back row.

I threw my scanners away years ago. You have the best scanner in the world with your digital camera. I do a lot of copy and restoration work and I have found that re photographing the piece that I am working on gets me a huge RAW file to work with, clean (no artifacts from the scanner) and the speed in which you can copy art works is about 20 times faster.

I love doing night images in my location (Minneapolis)

I use a flash with a small softbox to light my subject and then drag the shutter to bring in the buildings in the background. You will need a very sturdy tripod and I would suggest a cable release.

I would do two things before the big date:
- Know your locations, have two to three locations within minutes of each other, if it is cold your subjects will look cold, have them bring jackets to keep warm until you are ready to shoot.
- Practice shoot, go out there this week at night and shoot so you know what you are dealing with.