Slow down. Breathe.
Hi. First you are talking about sideloading. Now I know on my old Kobo, I just attached it to the computer and used the send to right click function.
I think most ereaders have wifi but you do not have to turn it on.
For questions about those two devices:
Here is the link to the Kobo forum:
https://www.mobileread.com/forums/forumdisplay.php?f=223
Here is the link to Pocketbook:
https://www.mobileread.com/forums/forumdisplay.php?f=206