My current layout is a 4x8 sheet of plywood, with the corners rounded off with a sabre saw. The platform in the video is 4'x6', we expanded it to 4x8 last year.
On30 is narrow gauge O scale, so simply put it's O gauge running on HO track... the 30 means 30 inches, or 2.5 feet between the rails in real life, but that's probably too much information

O gauge matches better to the holiday village buildings, but HO track is smaller and easier to fit on a sheet of plywood, so it's the perfect compromise.
I think you could probably get 2 loops of O scale in the same space, but I'm not certain.
ADDED: I'm using HO scale ez-track. It looks like fastrack but it's HO scale.
I played around in Anyrail with the Fastrack track library, and you can fit 2 loops on a 4x8 sheet of plywood. You can use 18" curves on the outer loop and 15" on the inner loop. It's tight, but you can make it fit.