Look.. all the "art" that you will be passing thru is better seen and read in books...So, what I would do, is take the red bus and do a scan of the city... then just put my walking shoes and get lost in the wonderful streets.. And I really mean the streets are wonderful.. and sit in a cafe, kiss your wife and watch the crowed going by and then kiss your wife again.. This is what Paris is..No worries about getting lost.. this is the funnest part of Paris, just walk and take turns into unknown streets..it is a very very safe city even at 4,5,6 am.. And find a metro or bus and they will help you..

This is what I would do. And do in any city I go to.