I wasn't sure if this would work automatically like most bulbs in a normal socket, or if I had to change something to make it directional?

Light will be emitted in the direction the face points to. In other words a face (side) will emit light to the side where you see a color or texture. Use the material name of each side to turn it into a light using the Library Editor lightSourceMaterialName property. A larger area will emit more light simply because there is a larger area to emit the light. Directing light is more difficult because you will have to create a housing that contains the light so it doesn't go where you don't want it, for example by putting an open cylinder around it. I don't think you need it with your panel.
If you use a room to create your panel it already has all around outward pointing faces (top,bottom,sides), all with the single material name room_1_1. Just export (only) the room and import it again. Tilt it 90° and give it a color. You will see that all sides get the same color and that are the faces that will emit light if you set it in the Library Editor. Just make sure that your level elevation is >0 otherwise you end up with a floor that has a height 0 and only the top will be a face that can be colored/texured, i.e. can be set as light.
On the other hand, that might be exactly what you want: just a single side that emits light. You can mirror a copy of the object for the other side of the gap in the brace. That's what I would do because it has the advantage that it renders faster and you can control the color and power setting for each side independently.

I couldn't drag and drop the brace. I had to import it with the button in the menu,

I have the same happening sometimes, I don't know why. Sometimes it helps to just save the library before adding more objects. That is the only reason I sometimes have to use the import button, otherwise I only use drag&drop. Try to drop in the empty area below or beside the columns.

I saved the item as a library and imported it into Sweet Home 3D, and it said it worked, but when the brace appeared in my file, it scaled way too large and out of the alignment I thought I'd set for it in the other files. I know I had scaled it much smaller (The same size as the old brace I was using), so I'm not sure what's going on there?

Maybe you mixed up mm and cm? I often create objects 10 or 100 times as big as they should be because the details are too small to edit in Sweet Home 3D. When you import it in the Library editor you can use the x10 or ÷10 to resize the object for usage in Sweet Home 3D without having to resize the actual object itself. You can see the values in the modify dialog when you click one of the buttons. You can also set a default elevation.

When you said, "You can use a different name for 'light'...

In the Library Editor you set the lightSourceMaterialName to the material name as it is in the obj/mtl files. Most existing light models use 'light' for the material name so you enter light as the value for the lightSourceMaterialName.
But sometimes you want multiple parts of the same object to act as a light, parts that have a different material name. You can multiple material names as the value for lightSourceMaterialName. Add multiple material names separated with a space. Be aware that multiple material names from the the same object will use a single power setting to control them all.