Currently the only way of figuring out how many slots does a cargo take, is to visit a warehouse or by try and error try to pack it, which not always is the preferable way, especially if the cargo if found in the wild, or we're nowhere close the warehouse.

Trying to examine a warehouse or an loose cargo looks like that

I'd propose expanding the pop-up with a slot counter, as a one seen at warehouse loading screen.

potentially a "Slots" word could be added to indicate clearer, at least for the loose cargo

Another example of warehouse
Currently:
Proposed (perhaps there would be a space for "Slots" word):
1.
2.
3.
4.

That's a really great idea!

In addition to this, the same should apply to factories. From the menu, once we see what the factory can manufacture, the pop-up menu should display the material icon aside from what we want to create.
From the Menu Factory, if we see that a Cabin can be made, the menu should display how many wooden planks and metal beans are necessary, and so on and so forth.

If we have a menu, why do we need to drive there every time to check what materials and how many we need to create cargo in the factory?

Let's work-wise!