How much work, and what sort of work, is an aspiring Torah scholar supposed to reduce?

 

In Avot 6:6 we find a list of 48 means of "acquiring Torah".  One of these is miyut sechorah (reducing the amount of business one conducts); another arguably involves some disengagement from money-earning: this is miyut derech eretz (reducing one's work, on the assumption that derech eretz here means that and not one of its other meanings: worldly activities and sexual intercourse). 

Rabbi Yaakov Emden observes in his Lechem Shamayim that there is another word for income-generating work, melachah, and that there is no corresponding requirement to reduce that. 

It is not clear to me exactly what the difference is between derech eretz and melachah in this context. Does any reader have any idea? Has anyone written on this? Please get in touch if you know.