At this stage gtfs2osm only synchronizes bus stops, not routes. I'm not sure yet how to tackle route import/sync, it is a much bigger challenge. Instead I spent some efforts improving PTNA: https://wiki.openstreetmap.org/wiki/Public_Transport_Network_Analysis

Size is not an issue. Israel has some 30k bus stops and the script handles it gracefully. I think even 170k is not going to be an issue, save for OSM rate limits.

If the GTFS data is reliable enough, the script can effectively import it the first time it's ran, and thereafter just keep OSM updated whenever new GTFS data is available.