The ideal place to shoot such a setup would be a set of risers (or bleachers) or a wide set of stairs, so to create multiple levels. Also, a hill would be a decent solution. If you could get hold of a cherry picker to get you up in the air (or even the top of a building looking down) you could stand them all close together looking up at you.
As far as lighting goes... natural light would likely be your best bet. If using flash (at least two strobes with WIDE brollies) I'd use it to augment natural light, not to be the only light source.
And remember to take LOTS of photos. People will blink, look away, yell at their kids to smile, etc, so more shots equals more chances of a "good" one to work with. Even so, with 60 people you're almost guaranteed to get someone doing any of the above no matter how many shots you take, so use the clone tool or copy in a "good" shot of them from another photo.
oooh, you're gonna need a tripod and lots of patience.
Here's the thing:
You can't crank the ISO up because you'll lose detail in noise. Especially important with THAT many people.
You can't open the aperture all the way up because you need a relatively deep DoF and also need to get the lens to it's sharpest point.
So, you either have to add light or run a longish shutter speed.
The longish shutter speed can be done. But you will have to let everyone know that if they move they will be blurred.
