I'm sure the shutdown procedure would be AC off first then DC. Its just to minimise arcing and thus help with the longevity of DC isolator.
The shutdown procedure is written on the white plaque on or near the inverter.
Startup is the opposite but I don't think it really matters.
Underneath one of the mid clamps should have been an Earth plate, when the new panel goes on, this one need to stay sitting in the correct position. This just pierces the oxide layer of the panel to attach the chassis to earth.
Just done my solar installer course, I know this stuff.