Hi Ron

1a: No, I've never removed a fender liner to replace plugs on an ML
1b:No, I don't think you'd NEED the Hazet wrench, it just makes it nicer for getting the plug wire metal ends disconnected from the plugs. You can try any open end 17mm wrench, but the Hazet wrench has an ideal offset to do the job.
2:Remove coils first, I do one bank at a time. There are diagrams on the coils to help make sure you reinstall the wires correctly. The "top" coil wire goes to the "front" spark plug. The reason I do it is to get the plug wires out of the way, and yes it may make the wires easier to get off the plugs. I'd rather not disconnect the wires from the coil, maybe you can try doing it that way instead.
3:No, as I said I've never seen the need to remove the fender liner.
4: YES, don't damage them
I usually disconnect the primary wiring (the single snap on connector) and set them aside. The rear one on the left and front one on the right have a nylon wire tie connecting the harness to it, if you want to snip the wire tie and then replace it when your done that's what I normally do, or if you want to just leave those connected you can do that too, it's YOUR truck!
5: never felt the need to torque those. Just reinstall them as tight as they were before:p

Gilly