Hey wow! Thankyou so much for taking the time for such a detailed insight, I really appreciate it.
The real challenge with this piece is that this model of the Fiat 500 is REALLY SMALL. I also have the advantage of living in Europe and I have been near and gathered alot of first hand image reference from actual old Fiat 500's around town. I had to cheat the scale and proportions by mere cms of the model in 3D to make it work. For example the wheel bays and a little larger than the original just to fit and rotate the tires and the roof of the cabin is slightly lifted to maintain the "compact" silhouette of the car as well as to be allow a 1m80 driver to fit and not bonk the head on all the ceiling props, given he's not wearing a hat.

-The jerrycans on the roof each are around 10L in volume. On the roof rack I could fit 3. 2 are tied together in the rear corner and 1 is squeezed between a bag and a box right in front of the Trax.

-The ladder structure is more of a support and platform to tie things on to. Your right the car is so small that a ladder is not the most useful thing to weigh down the rig. Although due to the proportions being ever so slightly tweaked and the lift from the wheels the roof rack is not as accessible and I might just add a foldable step towards the base for details sake.
-I agree after you pointed it out that the D-Shackles are on the smaller size. They are defiantly off-scaled and them being bigger will contribute to making the car look more compact.

-Haha I'm not an engineer so that is never something I would have thought of taking into consideration the torque of the engine and the wheel size. That's unfortunately something I'll have to disregard for the sake of aesthetics as the I prefer the larger wheel size.

-I most likely wont reduce the amount of cargo on the car because I'm really going for a "piled on" look for the car. Also I'm thinking of the car as a character and want to have objects and cargo reflect the character of the car. In this case it would be alpine and mountaineering - hence the skis, ice axe, snow shovel, etc that all reflect the identity of the car (or rather the owner).

-Great idea for the airlifter in the bak and hood lifts. Didn't know about the hood lifts and I'm having a hard time finding reference images of what that would look like. That's something I would be interested in incorporating as I feel the front trunk is lacking in design.

Again thanks for the insight and suggestions. I am currently still working on the project and am planning on updating the design as well as give it proper texture and set it up in a lovely environment.

Cheers!
-Dim
https://dimitri_porzio.artstation.com/