avoid long lines?

Louvre,, i go often, i never wait in long lines and I always go in high season. Secret is simple do not use main Pryamid entrance , use one through the shopping mall which you enter under the awning from Rue Du Rivoli,, you go downstair, buy ticket from machine,, there will stil be a security line, that is always unavoidable, but its about a 5 minute line if that usually. Orsay can be handled two ways. Go to Rodin Museum first, lines rarely any problem there, buy the Combo pass, it allows you SAME day admittance to Orsay ,, and with the Combo ticket in hand you will skip the long line at Orsay.
OR go to Orsay the day BEFORE and buy a ticket, you cannot use it on day of purchase but any other day, then you can just skip line with that, it is sold from a smaller ticket window at side as I recall,, but hopefully someone confirm.

The Louvre stays open late Wednesday evenings until 10:00. The Musee d'Orsay stays open late Thursday nights. If I remember correctly, the fee for admission is reduced after 6:00 on these nights. During my visit in 2009 I went on a Wednesday evening to the Louvre there was no line. I just walked up, purchased a ticket and went in. Last October I purchased a 2-day museum pass from the Office du Tourisme because I knew that I was planning to visit several museums. I went to the Musee d'Orsay during the early afternoon and there really was no line. Purchasing the museum pass was definitely a great decision. Even though you are on a tight schedule, you may want to consider it. It just depends on what attractions you are planning to visit and what your schedule is looking like. You can refer to the following website to obtain information regarding the attractions covered by the pass: www.parismuseumpass.fr Sorry, I am unable to answer your other questions.