Wrt to number 14, the metal grille; I think our cars had only one installed on the passenger side. This is confirmed by the parts books, as they give "1" as the corresponding usage.
When I disassembled mine, I noticed that the drivers side foot opening also has provisions to accept one, so I (incorrectly) assumed it needed one.
Just one is needed to be correct
A second one would on the drivers side would perhaps help to spread the hot air a bit, as during a long winter drive I sometimes felt like I was roasting my leg as the flow of air is quite concentrated.
Good to see the DIY thread is used, I'm honoured.
Let me know if you stumbled on something, and I'll try to improve it.