Once I cleaned up the front radiator support panel.
Bolt the new lower apron into position, with the lower bolts in the front guards.

This allowed me to check if everything was siting where it needed to be.

Final, push, shove, prod here and there.
(I spent a lot of time with panels on and off at this point)

Bolt up the doors, guards etc in position and tighten bolts

I then welded the front apron into position.

Once the front was in place, I then looked at working on the back end of the car.

Removing the rear quarters, let me just say.
I hope you like getting dirty and drilling/grinding.
I didn't count them all, but I'm sure someone on here knows exactly how many spot welds you will be un stitching.

Really take your time with this, it's important not to remove any more metal than needed.
I used a combination of drill bits, 4-5"grinder and an air belt sander to do this.

The section around the B pillar where the side vents go, I did little by little with a grinder.
You don't want to go at it hard.

My advice on the technique here.
Search YouTube for videos on removing spot welds.

Also, how spot welds are factory done, is very different than how you will do spot welds with your mig, 135amp mig will be plenty.

You should practice this with some scrap metal, even the old panels to get an idea on what settings your welder needs, AMPS/Wire speed etc..

When I do them, I mark out where I want them with a colour paint marker.

Lightly drill, the spots with about a 8mm drill bit, just until the point goes through the first panel, but not the whole 8mm bit going though.

This I think does two things for me.
I can hold the mig torch, square to my drill mark spot.
Then when I start the weld, the mig wire strikes the arc on the second panel.
They then fused together, as you fill up the small drill marking you made.
With the molten pool of metal.

Patience, practice and a lot of vies grip style clamps is all you need.

Hope that answers some things for you.

Cheers