What think about staying in 8th arrondissment ?

The Arc de Triomphe, Champs Elysees, and Madeleine are in the 8th, and metro and buses can easily take you anywhere else you want to go. Pretty much anywhere in central Paris will be good for sightseeing, no arrondissement is ideally located. The 8th may be the most expensive in the city though. You'll probably find better values for lodging and meals in the 4th, 5th, 7th, and others. Generally the closer you are to the river the easier it is to get to more sights on foot, and the more it will cost to stay there. As for cafes, they're everywhere, no need to look for them unless you have a particular one in mind.