120 Train Stations... in one general location

I'm going to attempt this and curious if anyone else has already attempted anything even remotely similar.

Do you have image samples of your build?

Lessons learned?

I'm planning to make the stations hidden in groups of walled off corridors to avoid frame rate issues as much as possible.

People told me don't do more than 8 cars for a train, they've told me don't attempt a central mega factory or you'll have to redo it a dozen times plus frame rate issues, they've said many things which just didn't come true. So, respectfully, I'm looking for someone with experience, not just what they think or heard.