16 bit. There aren't any 14-bit ADCs anywhere in LIGO. The aLIGO suspensions have 18-bit DACs.

The Y-End gains seem reasonable to me. I think that we only use TRX/Y as error signals once we have arm powers of >5 so we should consider if the SNR is good enough at that point; i.e. what would be the actual arm motion if we are limited only by the dark noise?

I seem to remember that the estimate for the ultimate arm power is ~200, considering that we have such high losses in the arms.