Upgrading from nook to kobo. Please help.

So I've had a nook forever and liked it but it's time to upgrade to the kobo h20.

Since I've had a nook for so long, I have close to 100 books. What is the easiest way at converting (preferably in bulk) to the kobo format?

I also view books via the nook app on the ipad. Doing a little research, people really like Marvin. Should I replace the nook app with Marvin?