Just for documentation, and to see if I'm finally getting this mess sorted right, a tentative report on how "zoned" and "dlc" industries connect to each other, please correct me if I'm getting anything wrong. I'll use farming as an example, but the other 3 seems to behave almost identically.

DLC industries have ploppable extractors, which produce "crops", ploppable processors, which transform "crops" into "animal products" and "flour", and ploppable unique industries, which makes those and their equivalent from the other DLC inds into "Unique Factory Products".

Peculiarly, "crops" is the only extracted product which goes directly into some Unique Factories.

Non-DLC has zonable growable extractors, which produce "grain" (seemly interchangeable with "crops"), zonable growable processors which transform "grain" into "food" and generic, non-zoned growable industries which make "food" and its counterparts into "goods".

Commercial buildings will sell either "Unique Products" or "goods". Boilers and Power Plants will consume "oil" and "coal", which are the respective intermediate products (before "goods") for oil and ore zoned industries.

DLC "warehouses" will take all their respective industries' extracted product (in this case either "crops" or "grain"), and nothing else. Non-DLC warehouses will take anything else, according to what is configured on their UI.

So, in order to have a complete, "no imports allowed", economy, you will have to setup zones and districts for all 8 different kinds of industries.

Non DLC growable extractors seem to be an awful lot less efficient (truck and spacewise) than their DLC counterparts (at least when combining Realistic Population and Industries Rebalanced), so it seems to be better to zone the non-dlc industries outside natural resource areas, in order to have them spawning only the processors (or skipping zoning altogether and use RICO to plop the growables).

On a side note, trucks seem to always spawn from the requestee building into the requester. So, from extractors to any processor (possibly via intermediate DLC warehouses), then from the processors to either generic "goods" industries, Unique Factories or Boilers/Power plants (again possibly trough non-DLC warehouse), then from those into Commercial areas or export.

Anything may be imported, except for DLC intermediate products and Unique Products, and everything can be exported. On this note, idk if it's vanilla or modded behavior, but generic growable industries will demand not only the "zoned products" (the results from non-dlc processors, which can be imported) but also the intermediate DLC products (eg. flour, or paper, etc, which cannot be imported), even if you never plop the respective processors, which will lead to building abandonment.

Again, please correct me if I'm getting anything wrong.

Edit: The DLC specific warehouses (barns, silos, etc) may be placed anywhere in the map, even outside their respective industry districts.