I used OSMRouter maybe 7 or 8 years ago to process a couple billion routes and it was about as simple as GP described. Just need Docker and an index file. the US one was massive so I kept needing a bigger VM just to load it, but once I did I was able to make HTTP calls over the network to get what I needed. Took a few days to get a working setup but only a few hours to rip through billions of requests, and I was making them synchronously with R; could have been much faster if I was smarter then.

Exactly. This isn't just a 10 minute project. And thats just for the website, not the tiles, etc.