The cost to buy directly from Tesla is $900 and change. So it can't hurt to upgrade since the dash is only installed on the CB. Typically they would not install on the AWD because it's not an OEM part for the AWD. Do it....
There are two horns tucked away in the wheel wells. When I had the frunk plastic tub removed you can access them very easy. I imagine they operate at 48v so if you replaced them with a 48v horn it might work. Splicing may have to be done unless you find the connector type. There are plenty of...
It looks like this is a set with the large one I already have from the foundation series and two visor ones. I'd buy if you'd offer just the visor shades.
I remember seeing a teardown video of the battery pack and it was not full of cells. Meaning Tesla could add more cells in the future. I don't remember if they used dummy cells or if the voids were filled with foam. They add foam to strengthen the battery pack since its structural.