What did you find hard about sideloading on the Kobo? I've had a Clara and now a Libra, sideloading books is as easy as plugging in a USB cable and clicking and dragging files onto it like it's a usb stick.
It's optional, but you can use Calibre with an extension to convert epub to kepub as well.
It's optional, but you can use Calibre with an extension to convert epub to kepub as well.