did all of these expansions reallocated land already held by the railways, or did some buy land to do it? how did they manage those in that case?

there are land acquisition issues, due to which we dont like to have multiple RoW for the same route. we also dont have marginally higher chance for freight derailment than passenger trains.

India? we do have general priority of pax over freight. but as soon as it is more than 2 tracks, we separate out freight (2 for pax, 1 for freight)

I'm sure that the point you are making is somewhat true, but this is the wrong comparison. (and also the wrong scale) India generally doesnt have rough mountains with coastal plains, while Southern China does, thats why development concentrates at the coast in (Southern) China.

Geographical map : google.com/maps/d/u/0/e...

Full res version : drive.google.com/file/d/1Kakm...

Diwali dinner... a month after Diwali?