Not sure who you directed comment to, but you have a lot of room for creative license.
Your primary scaling element is probably figures if you include them.
id think that based on your subject, you’d want access to, well, steam era railroad stuff.
So if you go O scale which is 1/48, your boat is 17” x 48 or 72 feet long. If you go with HO which is 1/87, your boat is 17” x 87 or 124 feet long. You can mess around with the deck houses using windows and doors from cheap plastic railroad building kits.
It sounds like a real fun project. I built a Nemo figure in a diving suit a little while back and had a great time.