Agree with Clare. You can't just leave a fallen camera on the floor, to be retrieved later. It needs to be found *right now* and secured. Especially if the lesson requires some abrupt maneuvering, like stalls, you don't want any loose equipment in the aircraft whatsoever. In most light aircraft the controls are not protected against loose objects. I know of at least one case where a pilot died because of a loose coin jammed a control run.
And there's one other thing. Setting up multiple cameras, lining them up, zooming them out properly and everything, and then removing them after the flight may easily take 5-10 minutes in total. More if you need to install cables as well. At my club, lessons are booked in two hour blocks, and instructors are paid by the block. You can't expect the aircraft to be available ahead of time, or afterwards. So setting up the cameras and removing them afterwards all need to happen inside that two hour block. So that time is going to be taken out of the time for the pre- and post-flight briefing, and the flying itself.
So whatever you do, make sure it's worth it. I would be OK with just quickly sticking a single camera behind you to film your control inputs and the instruments. I also really like the idea of filming the instructor while he/she flies the perfect circuit or another maneuver. But multiple cameras, audio input and whatnot? Overkill.