It's probably a matter of taste. Personally, I love to start in 1700 and get a business going. It's probably age-related as well; I'm 61 years old, and time has taught me patienceSabre_Justice wrote:While I know jack about coding, I have a feeling that if you want to make a more Industrial Revolution style OTTD game... it's probably possible, but you'd probably be better off building it from the ground up, at least with the economic system and payments and whatnot. I've tried it once and it gets frustrating very quickly with the slow vehicles and tiny loads, I'm sure some people love that but it makes it clear that the original and FIRS economies are both based around 20th century vehicles at least.

I've had a go at the FIRS source, but for now I've only set later introduction dates on several industries.
The Squid (FISH 2) ship set adjusts some parameters wrt ship transport, and actually makes it a lot more profitable to run the early sailing ships. Now I'm only missing a primitive barge available from 1700. It looks weird to run big sailing ships on rivers and canals.To get a 18th century game working, you'd probably want to adjust cargo amounts and payouts to reflect how everything is so short-range and even mail from the next town over is a valuable service, just for starters. Boats would probably be the only feasible large-scale transportation, and I can see heavy use of barges and sailing ships to get industry working.
I'm currently in a game in which, by 1824, I've got 267 RVs (mostly mail carriages), and 249 ships. So yes, ships are indeed the only feasible large-scale transportation.