So I learned that in order for me to have fun with Transport Fever 3, I need to apply a sort of triage procedure: Let go of the feeling that I should solve every problem, and tackle the problems in order of priority. What I said in my previous post on TF3 helps: Transport Fever 3's win condition is maximum population growth, not maximum money. And helpfully, every city displays after its population number an indicator of whether that city is currently growing. No indicator means no growth, a single arrow upwards means some growth, and a double arrow means fast growth. Thus it is relatively simple to quickly scroll across the whole map and check every city. Any city that isn't growing as fast as the others is a good starting point. You can then click on the city name and get the city overview, with its 8 parameters affecting city growth. Those are color coded green-yellow-red, showing you quickly what the reason for lower growth is.

The starting point for every city is the supplies parameter, with each city needing transported passengers, at least one industry good, and at least one commercial good. The more a city grows, the more of each they need, and from a certain point on, they need a second industry good and a second commercial good. Note that city growth is actually separate, if you provide for example only passengers, the residential area will grow, while without their respective goods delivered, the industry and commercial quarters won't grow as much. Nevertheless, for the start of the game the easiest way to get every single city starting to grow is to create two lines, one from residential to commercial, and one from residential to industry (note that circular lines doing both are possible for this, but tend to cause more traffic problems later). That internal passenger traffic counts for the first supply need, and your overall growth at the start is highest if every single city at least has that passenger demand fulfilled to some degree. Concentrating on a few big cities and just leaving smaller cities untouched is much worse for overall growth. After taking care of the first passengers, you can then check how far each city is from the goods it needs, and start by delivering the closest goods first. I wouldn't start on delivering the more advanced goods until all the demand for basic goods of all cities are fulfilled.

Fortunately, playing this way for maximum overall population growth also tends to work well for your finances. You might sometimes check the balance of all your lines, as putting too many vehicles on a line can result in negative finances. But overall, most lines that provide something that makes a city happier also result in a positive cashflow. Depending on how hard a difficulty you play, you get into a large surplus sooner or later. And then you can tackle problems like delivering needed goods from across the map. Which also is ultimately a money maker, but tends to require more capital outlay.