Doc,
I can answer all of those questions for you.
Is there a scale or gauge they are following?
Yes, it's 16" gauge, or roughly 1/3 scale. Actual 1/3 scale is somewhere between 15" and 16" gauge. Funny enough, 15" gauge is more popular than 16", but their first steamer was the green RGS 4-4-2 and since it was already 16" gauge that's what became the norm on the "full size" Whiskey River Railway.
Where do they get parts for those well maintained steamers?
Very few things are available commercially, so what isn't available they make in-house. They have a full machine shop to make anything.
Is it a coal or gas fired boiler?
They use both coal and #2 oil on their steamers and diesel in their diesels. When I used to ride along it was always more fun to take out the 1919 because you had to shovel coal, but easier to run the Oakland Acorn solo because it was oil.
In the video it looks like they run at 100 PSI. Is that correct?
The Oakland Acorn (the one in the cab shots) and the Gene Autry Special (not seen in this video, but if you look at the other WRRy videos it's the Daylight looking steamer) are essentially the same locomotive locomotive but just "dressed" differently, so a safe guess would be yes. Specifics like that I don't remember, and of course every locomotive is different like in 1:1 scale.
Is it privately or publicly owned?
It's privately owned and part of the Little A-Merrick-A Amusement Park in Marshall, WI. Between the railroad and their old Wild Mouse coaster, those are the two most unique aspects about the park. Their website is here:
http://www.littleamerricka.com/ and the Merrick Light Railway Equipment Works is here:
www.merrick-light-railway.com
Hope that answers your questions. I'm about to head to the train club today to check out what the guys are doing and BS like usual.
Tyler