I would say the best place to start passengers is castle town - gerudo. (tunnel into the pass from hyrule field. You will likely need to re-make the road once complete.) You can make a decant profit off a castle town tram alone as well.

freight is a bit more difficult but you can set up coal from gerudo the mountains with a bit of tricky track laying. Same for stone and grain. Oil should be done later. Same with ore. Wood has a nice loop but is also a long distance and requires some very expensive bridges.