The game seems very straight forward during the first 3 chapters which are basically tutorial levels and as long as you expanded your network faster than the AI, you'll fairly much win.
However, chapter 4 really puts what you learned to the test so here's how I managed to achieve the tougher objectives.
Bumping up Atlanta's population for the third set of objectives was the toughest this chapter. For Jacksonville, all you have to do is build a museum and that's enough to get the extra 10,000 you need. Atlanta on the other hand, feels like it doesn't grow at all during my first few attempts.
So, here's what I ended up doing.
I got to the third set of objectives by 1862 October in the game and decided to leave the 3000 Louisville to Atlanta migration last since it was the easiest.
If you have the capital at this stage you might want to max out Atlanta's station so that it has 4 tracks to use since you're going need a looot of supply routes.
First connect Knoxville and Atlanta. Make sure Knoxville has a good supply of cattle because they will be supplying meat to Atlanta. I connected up the Scott Ranch since it was closest without going through too much forestry or hills and Atlanta has no demand for cattle. Next connect Sawyer Cattle in the south because Atlanta has a high demand for milk to produce cheese.
You might be tempted to connect to the coal supply in the west because they need it for producing chemical exports but it's not worth it. It's expensive to plough through the forest and you can meet demand without it.
To meet the remaining lower demands that are only 0.7 or so, connect other resources such as wood in the west, corn and wheat from the east. Cities like Augusta in the east can also supply beer and cloth.
Be sure to use freight trains of course because they can move faster than express trains when loaded despite their lower max speed.
Once you've connected all the nearby resources and cities you should have a good cashflow going and have a good fulfilled demand rate. I got around 80% and cashflow hitting hundreds of thousands easily.
At this point, you can create a dedicated second station at Louisville and even Atlanta too for transporting passengers only by express. You can probably even build an attraction in Atlanta to help increase the number of passengers and that should be you!
For this chapter, gaining $600,000 profit in time was the toughest part.
To the north of Redding you'll notice there are 2 wheat fields. Connect these two up so that Redding has a big supply of wheat and it will automatically start its own beer industry. Next link it up to Gold Beach in the north.
Now you can go onto connecting the main cities that are in your objective, namely Sacramento and San Francisco to the west.
After that, connect the other basic resources such as wood from the east of Redding and corn to the south of San Francisco. Both Sacremento and San Francisco will have a high demand for cattle so you can connect up the cattle ranch to them. Let both cities share the corn field south of San Francisco since it's one of the basic resources they'll need to grow too.
If you have the spare funds, you can build a warehouse to the south and stockpile all the resources Sacremento doesn't need yet such as cotton and milk. Then you'll have them ready once the city has developed to the next level. You can do the same in the north so that Redding will also have resources ready and also make train journeys shorter for transporting produce.
Once the cities are developed to the next level and you've connected them to the warehouses, the profits should soar to $600,000. Prioritise spending your research points on ideas that will increase profit from freights will help. You won't need speedy trains before you've achieved the profit goal yet anyway. I only used the starting Philadelphia trains.
You'll probably have achieved the 100,000 population goals before the profit goal and even the optional goals of developing Sans Francisco.
As for transporting 50 passengers to transport from San Francisco to Promontory Point, as long as you've got at least 2 years it's not really a problem.
The key is buying the best express train and filling it up with staff. In my case I was using the Rogers American 4-4-0. This will boost it's top speed to around 90km/h but if you also spend research Caboose carriages then add them to the train, it goes up to 130km/h and really speeds things up!
Well, hope that helps anyone that struggled with these last two levels of the campaign!