Welcome to MobileRead!
Yes, Calibre is an invaluable piece of software. I buy a lot of ebooks from various stores and use Calibre to manage my library basically every day.
(As to the DRM removal... yes, it's still possible to remove the DRM from ebooks, even from Kindle books. In the latter case it's not as simple as it used to be, though. Amazon tries to actively stop DRM removal from their books, so you have to constantly jump through hoops and find workarounds. This site is actually the best place to get information about the latest developments.
It's also possible (and quite simple) to remove the DRM from ebooks bought from Kobo, Google Play and B&N. AFAIK the only store where DRM removal is not currently possible is the Apple bookstore).
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