Museum pass for month stay

This is an interesting question so I googled it. The Paris Museum Pass can be purchased for 2, 4 or 6 days. For longer stays the site recommends checking into subscription options that are available at several museums, i.e. the Pompidou Centre (Laissez-passer), the Louvre (Carte Louvre Jeunes, Amis du Louvre), the Orsay museum (Carte Blanche), etc. For more information about these options consult the website of each museum. Good question. Hope you have a wonderful time in Paris!

Unless anything has changed in the last couple of years, you must use the Museum Pass on consecutive days. If your first day of using it is on November 1, for example, the other five days of use must be from the 2nd through the 6th. You'll have to do the math to see if it's worth buying more than one pass, depending on how many museums you want to visit.

Yes, the Paris Museum Pass is offered just for periods of 2, 4, or 6 consecutive days that start with your first visit.

Looks like you are going to enjoy a "museum week" on your trip! A couple of things to add: most museums are closed on either Monday or Tuesday, so I would assume these would be the most crowded days as people go to the ones that are opened on those days (I would think especially Versailles if you are planning to visit there). So start your pass on Wednesday. Also, many of the museums are free on the first Sunday of the month if you arrive in Paris by then. Enjoy!

Because of the crowds, the Louvre no longer has free first Sundays from April through September. I believe that is true at the Orsay as well, although I couldn't find any mention about that on their website. To avoid waiting in a long line, you should probably buy your Orsay ticket in advance. You don't need to do that at the Louvre, although there is always a large line waiting to go through security. I don't know of any month-long museum pass.

Another idea, thanks to my husband for reminding me of this. The city of Paris has a number of museums that are free to the public. My favorites of these are the Petit Palais, the Musée de l'Art Moderne, and the Victor Hugo museum. There are many others. Here is a link to the list:
http://www.paris.fr/english/museums/municipal-museums/p8229

If either of you is a teacher of any sort, you can get a membership for 35 Euro that allows unlimited visits to the Louvre and also allows you to bring a guest on Weds or Friday nights.

For the Orsay get tickets ahead so you can use the entrance for people with tickets as this is reliably the most difficult line at entrance. for the rest for a month, I wouldn't use the pass but would save museum visits for days the weather is less pleasant outside.