I've removed a couple of them in my time. What you have written is a good basic guide. You are right in thinking that you will also need to unpick it at the door pillar and along the bottom (including around the wheel arch).

What may help you is to get hold of your replacement quarter/s first and this will be a good reference at to where the panel starts and ends (e.g. the top of it will run behind the side vents etc.)

Get youself a proper spot weld drill bit from you local Autopaint store. These bits will basically drill a small circle around the spot weld and enable the panel to pull away from the weld, hopefully leaving the underlying metal in place...however from time to time you'll probably find it may drill a hole through both layers of metal (nothing that can't be welded up).

At times it is helpful to cut large sections of the old quarter panel out with an angle grinder and that way you can wiggle the sections near the spot welds to help them breakaway. CAUTION WITH THIS AS THERE ARE SOME THINGS LIKE THE FUEL EXPANSION TANK AND FUEL FILLER SURROUND THAT YOU DONT WANT TO CUT THROUGH IN THE PROCESS.

I found around the wheel arch it was best just to grind away at the metal with an angle grinder and pry sections off with a screwdriver or chisel.

As far as re-attaching the new one it was a matter of drilling holes along the edges of the new quarter panel (about every 70mm) and then plug welding with a MIG. You'd probably want a MIG of around 160 AMP or a little more. The other option these days is to use a panel adhesive and just glue them on. Oh, I also used a bead of Sikaflex urethane sealer in between the plug welds.

GOOD LUCK