I unexpectedly find myself the owner of both a Nook and a Kindle (buttons, not touch screen) after the Boy decided he really didn't like it after all. A couple of questions for ya'll as I completely know how to work my Nook including DRM with Calibre and the like.

Can I put my Kobo purchases on the Kindle via Calibre? Additional plug in from Apprentice Alf required or no? If I have Amazon purchases in Calibre that I have converted to ePub and now have both Mobi and ePub, can I load those back on to the Kindle via USB?

How do I deregister the Kindle from his account and register it on mine?

Thanks!

Anything you can convert to Mobi format can be put on the Kindle and recognized. It's the conversion choice just under Epub. Apprentice Alf does Kobo as well. 

You need to go to his account, go to "Manage your Content and Devices", Then "Manage Your Devices" and if he has more than one chose the Kindle. There should be a down arrow to the left that says "Manage this device". click it, then to the left is Deregister.

Have him Deregister the Kindle and you can then register it to your account when you turn it on to shop. I'm not sure what the process is to register the non-touch ones. 

With the kindle, from home screen press menu.  Select Settings.  Then press menu again.  That will bring up the registration option.

If you have Calibre set up to free adobe library books, that is all you need for Kobo books. At least the ones I get. They open with adobe. Then with Calibre I go to the My Digital Editions folder and load the book. Then you can put it on your Kindle or Nook.