When is the right time to do a scholar-only run?
You can't stand all disaster you need to at least protect your scholars.So you always need other people that you sacrifice for the disaster effect.

But if a lot of disaster are in the beginning of the year this can be possible. Also you need to play against beginner player as experienced players will block you or do more point than you , by having more room than you. 

Getting the geisha soon is also a plus for this strategy.

I've already see someone win by this strategy but more often they will fail. In my opinion you need to mix other source point to achieve victory.