Which openwrt-packages for EC25 serial required (MIFI)?

I need to build a custom image for the MIFI incl. EC25 from latest official openwrt sources.
As I want stability, because of unattended operations, and not highest speed for the WWAN, serial connection to be used.
Which packages I will need to install (kernel moules, USB, 3g …) ?

You can refer to OpenWRT docs.