Skip the line tours

We buy tickets ahead of time ( or in Paris , the Paris Museum pass) and then use audio guides whenever possible. It is less expensive and we can go at our own pace.

I would buy skip the line for the Catacombs (buy directly from the website to book your time slot) because that line can be a 3-4 hour wait. Eiffel tower you would book your time slot ahead of time, again with the official site (just saw your going next week, these should be purchased up to 90 days before you go) and the Louvre is not that long of a wait for a skip the line advantage and you never skip security which could have a line.

No. They have access to the same tickets but just charge more and then herd you through at a pace unlikely to be your preferred pace. Just get your own ticket well ahead for the Eiffel Tower and catacombs. The Louvre rarely is an access problem they have a couple dozen machines that sell tickets in the lobby and the security line at the Carrousel entrance is usually not that long. You can get a timed Louvre ticket that grants you access at the pyramid at your time.

I purchased tickets for the Catacombs at headout.com two days prior to our arrival in Paris earlier this month, and was SO glad I did, we literally waited only 5 minutes to walk in the door while those without tickets queued in a line that went around the block. Just note that the tickets are timed (i.e. you purchase a ticket for 3pm entry and you must show up between 3pm and 4pm) so you have to have a good idea of EXACTLY when you will be there.

Figure out WHAT you want to see, and whether the Paris Museum Pass would be cost-effective for your needs and time. In many/most cases, there's a pass-holder line which is faster than the general entry line. If you only want to visit a few places, individual timed tickets might be better.
Eiffel Tower -- think you missed the window for direct-purchase tickets. But you can look AT the Tower for free.

And no tickets required to just walk through the streets of Paris. Enjoy!