the Guardian

Well, it's your wild idea. You're going to have to figure it out for yourself.

You can hand lay track using whatever rail stock you imagine is appropriate and you can make your own ties or buy some from garden railway suppliers. People who are serious garden railway hobbyists do it, so it's not a far fetched idea. Lots of information out there on that topic.

As for the train, you'll have to have some advanced modeling skills, either to build something from scratch or convert some 1:32, 1:29, 1:24 or 1:22.5 scale equipment to match your vision.

paigetrain,

Jim R is correct in that you'll need to scratch build or modify an existing model to meet you needs.  I hadn't heard of the "Guardian" before so I'm not familiar with it outside of the description in your initial post.   The locomotive could be assembled from a couple of old Marx engines for the powertrain and the shells would require some extensive work near the front.  But this is a doable project.  As for the cars, you'll need to be creative there as it could get expensive if you want aluminum sides.  But I would start with some long flat bed cars and get some scribed wood sheeting at the hobby shop and build my own cars.  Since this is an imaginary train, you can design it to look anyway you like.

Not sure of who your pictured friend is, but the portrait is very well done in terms of lighting and capturing the models intense expression.