* My vague recollection is that towns and cities need about two loads of each cargo in each 2-year cycle to help them grow. Demand softening and recovery is independent from that growth mechanism.
* Industries generally conserve cargo car count, so if you supply 2 steel + 1 tire to an auto factory, then you'll get 3 cars out.
* Unpatched, only the top port demand will recover. That's a bug. The simplest repair is to edit your map to put the most important trade in the top slot of the map's port definition. Other threads on this site explain how to patch ports completely, but I think they have to be fixed one map at a time.
* If you are investing in industries, then you have a trade-off. You can either trade slow to maximize delivery profit, or you can trade fast so certain buildings "gush cash" (buy them first).
* Pax & mail are the big money makers in the game. Sadly, cargo is usually unprofitable. However:
* Haul slow heavy cargoes only short distances. Be willing to accept losses needed to produce fast cargoes that profit from longer hauls.
* Also be willing to accept losses needed to supply town and cities with the cargoes that will grow your pax & mail.
* Towns and cities come in different sizes, so your pax & mail "pairings" will be uneven. What you want is balance of house-count (i.e. 1 city with 12 houses can balance 3 towns of 4 each on the other side of the map).
As you play, you'll become more familiar than my now-fuzzy memory, so please post discoveries and epiphanies back to your own thread.