Hi,
The Louvre is probably one of the most photog friendly place ... as long as you don't use flash, it's fine in most of the rooms (only temp exhibitions do not allow any picts).
Orsay has changed policy lately into a "strictly no photo policy" and got lots of complains (some special photog protests aka "flash mobs" ... not Speedlight, but "fast" protests...;-) )
Usually only small bags are allowed, aka purse or similar (so that you don't damage the art objects) ...
Inside churches in general, they often request no flash...
Build your visit list, check the museum/places websites before, and if you are unsure on some places, send me a private message in advance of your trip and i can check some for you.