They'll learn the hard way.
I can always put a note in the briefing, or I can add an explanatory dialogue when they cross the first threshold.
I have this thing playing well now, on the whole. I'll adjust the overall building growth rate curve, as I think the scenario is still getting a bit too big, a bit too fast. It needs to be "hollowed out" somewhat in the mid game. I'm may also adjust basic building density and/or express production on some of the tiny towns way out west. The Goulburn-Yass-Galong line has scant traffic, wheres IRL it was a major artery that linked Melbourne and Sydney, so a moderate boost to express production would make sense there.
The other case is the area around Sydney. Due to the closely spaced cities and good links with Newcastle and the South Coast, pax numbers in the Sydney area get absolutely mental by 1870. Admittedly I am using hotels in most cities there, but I'm not spamming them with multiple hotels per city. It has me thinking that once you are out of the earliest years, and providing you kept a minimal number of freight trains to handle essential haulage just for track bonuses, etc, it might be possible to play this almost as a pure express map for a change.
That could be an interesting challenge. There is a lot of scope for express routing once things get going, and it can be highly lucrative. The regular Parramatta-Newcastle express trains hauled by a 14 Class often haul trains worth $300-400k each. Other 14's running around the Sydney area can return $150-200k per year, even when the high pax numbers drop individual cars prices there to quite low levels.
Which reminds me: I have been tweaking the loco stats for the NSWGR roster. I was looking at the way things were performing a couple of days ago, and there were issues. The 14 Class was too strong up hills, so had to be adjusted with more free weight and less pulling power. There wasn't enough differentiation between the 6N and 17 classes either, so that needs tweaking too. That got me thinking about your old points regarding fuel usage in this era. With the low car weights necessary for a good progression over 200 years, the early locos have to be low in weight as well if the effects of loco weight are not to outweigh consist variations. That means we need the high fuel ratings to get good differentiation between classes in this era. So yes, you were right.
I've set my RT3.lng so that, in terms of display, the lowest rating is Very Poor. The text for that is duplicated in the language strings for the old lower ratings (Atrocious and Extremely Poor). This lets me use any numbers I like without every loco being "Atrocious", which is a term that puts me off, and which I think would put other people off too. The 14 Class and 23 Class fuel economy has been boosted to 13 and the 8 Class 2-2-2WT has been boosted to 18. They're still perfectly good and profitable express locos in this scenario (it raises annual running costs by around 50%/$10k). Loco stats are still evolving, but are looking better all the time.
Note to self: these higher fuel ratings will require an adjustment to the event that emulates "lower fuel costs" as a percentage of company overhead.
Another note, to anyone: I'm finding this map lends itself to "stack and dump" tactics once things get rolling. Freight trains could probably be used exclusively for stack and dump tricks, with no regular freight runs at all, and all the regular runs (apart from the wool trains) being express only. This may be the most lucrative way of handling the map.
In my latest play I also went with a double station at Parramatta. Parramatta is normally a major bottleneck. Splitting traffic between two stations seems to improve things markedly for minimal cost. I put them right next to each other on the same line. The standard station handles all traffic from the line that runs via Liverpool out to Yass, as well as traffic on the Penrith - Richmond - Windsor circuit and the Blue Mountains line. The second Parramatta station, just to the east of the first one, handles traffic on the Sydney - Hurstville - South Coast lines, as well as traffic coming down from Newcastle and Gosford. This ends up being a roughly equal split for traffic, and works very well. Once that section is double tracked four trains can pull into the two stations simultaneously and unload, without interfering with each other. It makes a big difference.
Naturally I'm also using a bypass that runs from the bridge just west of Penrith, direct to a second station in the Sydney Port territory. IOW, it skips the whole Penrith - Parramatta - Sydney line entirely, and lets wool trains go direct to the port once they are past the Blue Mountains. Same deal: heaps better traffic flow once wool trains start rolling in. Wool trains from Yass come down the Moss Vale - Wollongong line, then bypass Hurstville and go straight to the port station. Once you have enough track to get away with building these bypasses they are well worth having.
