I think I may be able to help out on your question regarding concerts in Paris. When in Paris last March I attended a chamber concert held at La Sainte Chapelle. These concerts are widely advertised, cost 25 euros, and feature popular programs like Vivali's Four Seasons and Pachelbel's Cannon. Ours was performed by Orchestre les Archets de Paris. The setting was beautiful but unfortunately the music was a bit disappointing. The orchestra didn't seem that proficient or well rehearsed and it showed. Perhaps it was just an off night - Conversely, I once attended a similar program at London's St. Martin in the Fields. That concert is one of my fondest travel memories.

Have a wonderful trip, Dawn Philadelphia, PA