I wish you could just download a big bunch of pre-rendered tiles for each country.
b) the more sensible approach would be to use pre-generated vector tiles, for example from https://openmaptiles.org/
Now we just have to periodically take a fresh pull of the tile package, so our tiles aren't too out of date.
Or build your own from planet.osm (that's a file, not a domain (it's hard to tell these days)).