As others have said, both are great. Some bits of the first book may be obsoleted by newer language features, but will still give insight into why these features came to be. Also note, in my impression, Effective Modern C++ is pretty hard if you are not quite familiar with C++11 already.

Keep in mind, Effective Modern C++ is not a good book to learn modern C++. You learn modern C++ (11/14/17) from other resources and then come to this book to read about quirks and corner cases.

Yes. Effective Modern C++ covers the new features, but doesn't repeat what is still valid and in use on the features that were there before.

Yes. You miss a lot. Effective Modern C++ is not an update of the original. It's more of a supplement that covers the new stuff.

In addition to the other replies, you might end up working on a codebase that precedes C++11.