I’ve had a lot of success with passenger trains that connect multiple cities combined with local bus or tram traffic in each city.
I normally start by connecting 3 cities (in 1850 start) with double track. You need to buy multiple trains to keep the frequency down. The first trains are so slow that the frequency needs to be high to keep the total travel time low. As the train speeds and passenger capacity goes up, I add more cities to the line, going up to 5. This you can do when you get the first 100 km/h train. Also you can afford to have a bit lower frequency as you get faster trains because the total travel time remains the same.
I’ll try to make a guide with screenshots some day this week 🙂