Thanks for your answers !
I'll look at the KSM configuration for auto start.
I've just read issue 1234 on GitHub, maybe I will try to help by enabling log as explained.
As far as I remember, the device's backlight button don't work when in KSM. I must check that.
KSM USB mode is fine indeed, but I think about "mainstream" users. My wife has a Kobo Glo too, but finds that KSM is a bit too involved or geeky for her. So my questions (dict issue, auto start and USB mode from within KOReader) are about trying to avoid KSM completely.
About battery, I've collected daily statistics since a month and a half. All I can say for now, is that the battery lifetime is no more what it was when I bought the brand new device
But it seems rather consistent between the 2 suspend scripts. Nowadays I'm not reading a lot, so the device usage is pretty low, and it's kinda long to deplete the battery. In one month and a half, I've charged it only three times. One charge lasts between 10 and 15 days for me. I don't think proper stats could emerge from 3 samples...