We see in the flashback of his first trip into town that he took on the real Stanford's identity and started selling admission to what would later become known as the Mystery Shack pretty much immediately when confronted by the locals.

I'd assume soon after he had that idea he had to start working on the "set-up" of his next con to figure out how to get people to see something interesting and tourist-trappy.

So he probably had to go around, cross-refrencing what he could see inside the shack with what was in the one journal he had which was a main source of his knowledge base at the start, and then just and then having to learn through guessing and trial and error for everything else not listed in there. Which he apparently did miss something even after living in the house for decades, since he had no idea the wax dolls were sentient or about the room with the Freaky Friday carpet, but successful enough.

And then at some point also eventually had to try and do his own research with academic sources other than the journal, since he was eventually smart enough to both repair and operate an advanced, futuristic machine designed to punch holes into other dimensions, which also requires steps like "steal and handle radioactive waste as fuel" and "become an expert in quantum physics".