If you choose C array format 8, 16 and 32 bit outputs will be included in the result C file. For binary output you can directly specify the format.
The order of color channels in the array is Blue, Green, Red, Alpha.
You can read more about it here.
It’s the alpha (opacity) channel. It always there in 32 bit color depth. However, for 16 and 8 bit it’s added only if True color with alpha format is selected.
Yes, on the above-mentioned link.