Hi. This is my first post other than my introduction. I would say my current proficiency level is "student" but I'm motivated to bootstrap my understanding fast and get to making things.  This is also an "excuse" to expand my workshop.  

(using the photo included above for reference)
My current "side-side-mini-project" is to produce 1966 Mustang fastback styled louvers (pictured above) for my 1967 Mustang fastback sail panel. The panel shape changed fairly drastically between 1966 and 1967. So to pull this off, I'm going to be making a custom panel and I want the finished product to be carbon fiber. That goal is what brought me here in the first place.

(so that's the context for this)

Would anybody be able to provide the pattern making process they might use for themselves if they were producing this as a one-piece composite part? The originals are a single pot metal casting. 

Here is what I'm currently doing and have done:
I started by cutting up a spare Amazon box and eyeballing in a roughed in perpendicular mock, mostly so I could get a gauge of just how much off of perpendicular I would be dealing with.

For the first pattern, I have the louvers removed from my sail panel and I'm currently working with crafting polystyrene foam to try and get the panel shape represented in situ. I was able to get a fairly large sheet for 75c after a retailer deleted its SKU and was clearing the shelf. Since this is polystyrene instead of PE foam, I expect that I'm going to skim over this with Bondo to produce a smoothed, workable surface.

I am building it up like a jigsaw puzzle, sawing the foam into blocks and sanding on the eccentricities of the shape of the metal recess that needs to receive them. Rounding over the rear corners, chamfering the back edges, and doing my level best to sand the body line into the leading edge.  I've got spray adhesive that I will be tacking the pieces together so that I can remove it out from the panel recess as a single piece. Once I have it on the bench, that's when I'll skim it smooth with Bondo, so that I can 3D Scan it in and send it to my CNC Router to replicate the master in epoxy tooling board so that I can further refine the details of the pattern.

Once I can get to that point, I will need to obviously make a mold but that is my current plan for the pattern.  
Does anyone see anything I'm doing in my pattern description that:

a) is flat out wrong-headed?
b) could be improved?
c) is unnecessary?

[edit: fixed some formatting to prevent emojis]

Nothing wrong with what you are doing, except for that fact that if you are using expanded polystyrene (EPS) foam then styrene based body filler like Bondo will attack it. If it is extruded polystyrene (XPS) then it may be ok, though you will want to do a test first as I've been caught out by low quality XPS in the past.

So as you might tell from the timestamps of my updates, this is a very 'slow burn' project.

I have to build my cnc and my 3d scanner and run a vacuum line to my spare oven before I can get everything completed the way I have laid out. With work, family, activities for two kids, land, horses, and 2 Mustangs to work on, this is a passion project and fights for time with a lot of other things.

I'll be putting the scanner together soon. I've got all the equipment ready for it.

But...here is the latest progress on the plug:

Looks like a great scan, what did you use for that?

So the glue just dried on my latest iteration earlier today.  Hopefully, this helps tie with the visuals from the earlier version and give a better idea of what I'm going for. The "blocks" from the earlier version intended to represent the surface of each louver vane as well as reserve the space for the standoff of each louver from the next. That one was mostly an art project; this one I'm seriously hoping to take to the mold making process.

I made a frame like before, but this time I used my saw to slice 1/8" planks which allows for a MUCH thinner frame.

There is a space near the fore and aft of the panel that will have to be filled to finish the whole thing out. But here's where I am.

I still need to pin the louvers in place to set the position of the bosses then I need to remove my guide rails (white).

Then...it'll be time to skim with a surfacer and prep for a mold.

Here are some up to date shots of my current iteration of the pattern sitting in position on my car. I've still got to fiddle with some fine tuning of the shape and I've got to add a final surface layer, but I'm closing in on having something presentable.

Materials are JB-Weld, eps sealed with wood glue, chicken wire (unsure of gauge. It's literally some scrap chicken wire), and foamcore. I'll be epoxying #4 and #5 in an hour or so to get the cure started,  then time for a final surface layer over the epoxy.

As you can tell from the timestamps on my posts, life happened but I've never abandoned the project.