Anon offers a harsh truth

OP has no ambition, you can buy rolling stock for scrap value quite easily. If you have an insane amount of labour at your disposal you can do most things for a small heritage railroad by hand. The know-how is not secret arcane knowledge. The main issue is that most countries don't have that many enthusiasts willing to fund those projects. Road subsidies are insanely high but hurr-durr trains are expensive.