Behringer x32 Out 1-16 levels

1. I think so, yes. Route both L and R to one matrix bus, and assign that to Out 1.

2. That depends on how you provide a signal to the Out port: Out 1-16 is just the output assignment. You set the volume on the channel that feeds the output. This can be the mains, but also any of the buses, an Aux bus or a matrix.

You're comparing apples and oranges:

• volume through your speakers has to be "loud enough" for the room. This is mostly unrelated to the maximum volume that can be produced by the console; you can use the amplifier to adjust the speaker volume.
• the camera input needs a certain level.

As you've discovered, you need to be able to control room volume and camera input level independently. There are several ways to do this. The simplest is to route the Mains to a matrix, and assign that matrix to Out 1.