The 7th arrondissement is perhaps the most expensive area to live in Paris, the Eiffel Tower, one of the most famous tourist sites in the world, is located here, as well as many government buildings like ministries, the National Assembly and others. Many dignitaries and VIPs prefer to live in this arrondissement.
The Champs-Elysées is very lively and not too risky, at least during the day. You should still be careful on this large avenue, especially at night because it's so crowded that it is the perfect place for pickpockets.