my first thought is to use Add16 (seems most logical choice), but since b input has to be 16 bits, when I call Add16, do i need to set b=0000000000000001, or just b=1
Just like you can say "in=in[0]" in your Not16, you can use [] syntax on the left side of =.
Write "b[0]=true, b[1..15]=false" to set b to 0000000000000001.
Note that "true" and "false" a a bit magic in that they match the bus width that they are connected to.