I bought a second one for my husband last August. I registered his on his computer with the same Apple registration password as mine so we can share apps, IOW not rebuy. The app store will just ask you for the password and reinstall on the second Ipad
For Kindle I did the same. Same CC, same password but listed one as Diane's Ipad and one as David's plus I have a Touch the books sync with. So you only buy once. The Ipad that didn't buy the book will probably have to check its archives and check it to download, but that takes seconds.
Diane