Pretty simple instructions. Install the Obok plugin and restart calibre. It should automagically locate the kepub directory used by Kobo's Desktop app. Please note that Kobo Plus subscription loans are not supported.
A .acsm file is an Adobe Content Server Message file. You will need to open it with ADE or use the ASCM plugin. See the
ACSM input plugin thread for more information.
As for porting from Kobo? I'm not what you mean by that.