You could learn something about differences between epub and kepub (the second has no ligatures but is better for everything else, especially if the book has notes or imagines, in kepub a rapid double tip in the imagine can enlarge it). the issue is explained in the forum.
With calibre You can handle collections and many others thing like subtitles and others metadata in Kobo.
About collections:
https://wiki.mobileread.com/wiki/Kob...nd_Collections
Shelves and collections are the same thing, a book can belong to several collections.
For privacy in setting option there is the possibility to settle a PIN number to avoid that someone else could use the device.
The cover when the device is sleeping or is off can be settled with a little trick:
https://www.mobileread.com/forums/sh...d.php?t=321609
Finally: convert Your mobi file into epub (or kepub), mobi file are terribly formatted in Kobo. And download calibre from the official page, don't use the version provided by Your Linux distribution (this is recommended by the creator of calibre).