Having trouble understanding a basic MOS OpAmp diagram

Taken from: Analysis and Design of Analog Integrated Circuits, 4th Edition by Paul R. Gray , Paul J. Hurst, Stephen H. Lewis, Robert G. Meyer. Page unknown.

Hi. I am studying about MOSFETs and I am trying to understand what each component does in this circuit. I am having trouble however with transistor Q16. From left to right, we have a cascode current mirror, the differential pMOS pair with its tail, the capacitor for the feedback effect and a voltage follower Q8 in the output biased by the current mirror Q7&Q9. Now, Q16 confuses me. It looks like a common gate amplifier but I am not sure what it does for this circuit. So my questions are:

1. Do the Q6 and Q7 transistors amplify the signal?
2. What is the use of the Q16 transistor?
3. What do the numbers on each transistor mean? I think this is the W of the MOS but what are the units? Given the technology (CMOS 1.2μm, 5 Volt, 1 poly, 3 metals) I have L as 1.2μm, right? Is the W in μm as well?

Thanks!