Well congratulations on getting two new devices for Christmas!!
I'm not the best person to answer your questions but I can say that I just use Calibre's own program to convert Amazon's ebooks to epub, and I think that that's what the majority of Kobo folk do.
Then I sideload the book to my Kobo device and read away.
Other folk here will help you with attributes such as Book Shelves and fine tuning your use of the device with plug ins etc.
Also, you need to be aware that Kobo uses two ebook formats - kepub and epub.
The kepub format is Kobo's proprietary ebook format that is used to sync the device between the Kobo server and Kobo apps and the Desktop for Kobo.
When you buy a Kobo book you usually get a choice to download the epub version (go to My Library on the kobobooks.com site). If there's no download option then it's a kepub only book, which means that you can only get the book onto your device by syncing your device with the desktop, or by using the wifi feature on the device, or by using obok. Here is the address to download obok, and the Article also describes what it does:
The Digital Reader
The instructions for getting obok into Calibre are also in that Article.
Keep asking questions as you need to, and happy reading ...
Edit
I nearly forgot ... the most important thing you need to know is to follow the
Kobo Discounts thread to get all the latest info on the discount codes that work and (usually) monthly Contest info!!