I can't quite understand the three panels, stationary panels and two sides of one window....?

This is a photo of my bay window wall.

I am thinking of placing 1 standard width panel (approx 54") on the left and right far wall sides. The wall space surrounding the middle is 50" on each side. I was planning on having 2-3 standard width panels sewn together on each 50" inch area. I need advice on whether I should do 2 or 3 panels on this area to achieve proper fullness.

You are correct that 2 widths are too skimpy on your 50" wall spaces. 2.5 or 3 widths will give you appropriate fullness

The photo of the drapery you like is a panel consisting of a width and a half.

I would recommend finding a workroom in your area. I would do the 2 outside panels@1.5 widths each and 2 larger panels@2.5 or 3 widths each.

Not knowing you ceiling height, I would guesstimate 24-27 yards of fabric.

I take it you are making these pleated panels yourself. Figure on getting one 24" -27" (measured across the top) wide panel from a 54"-60" wide fabric piece. The top width will be even less if you want really deep folds. I don't think you need to sew the pieces together if these are stationary dummy panels. Just make individual pleated panels. I think you'll need three between each window to get the fullness you desire. BTW, to get the folds as shown in your inspiration photo, the curtains will need corner weights and you'll need to train them to hang properly.

I like your vision for this window wall, btw. :)

A couple years ago, I made a Two-finger Euro Pleat (pinched at the top) center draw drapery for a room in my home. I looked up Parisian pleat and it's described as a three-finger pleat pinched at the top. Here are my details in case it helps you...

My window width is 94".

Fabric is 54" wide.

For each half of the window, I used 2 widths of fabric.

For one panel (2 widths of fabric sewn together), I made 12 pleats.

Per panel, I used 4 1/2" pleats, 4" spaces, 3" return (the distance from the face of the rod to the wall or
casing where the bracket is attached. The amount of
drapery that covers the space between the rod and the wall.), 4" for center overlap.

4 1/2" was good for a two finger pleat. I would likely have needed more than that for a three finger pleat.

The stack back (fullness when drapery is drawn open) is about 16".

I used black out lining which may be adding some fullness to the stack back.

My seam happened to be inside one of the spaces between the pleats. I didn't plan it.