> But I'd be very very worried about not having a little put by each
> month, in case of emergencies. 

http://www.daijob.com/dj4/en/column/terrie/index.jsp

This man (in article 78) puts food at about 60,000 a month. I suppose if 
you're very busy, food can be expensive because you don't have time to 
plan properly. Hopefully with part-time work I will have the time to be 
frugal. Also I'm not much of a meat eater, or a big eater in general.

As for emergency money, I have thousands of $ in savings so I should be 
able to spend every yen I earn with a clear conscience.