First Solo Trip to Paris - Itinerary Help

I would shufffle things around a bit, and get a 2 day Paris Museum Pass (48€) for Mon/Tue.
http://en.parismuseumpass.com
Due to the potential for time wasted in line for the Catacombs as well as getting up the Tower at Montparnasse, I would reconsider these two inclusions.

Sunday pm
•Notre Dame
•Wander the Marais, visiting Place des Vosges
•Seine Cruise from Pont Neuf

Monday
•Arc de Triomphe* (Opens 10am)
•metro line 1 to Concorde, then walking ...
•Madeleine >> Palais Garnier Opera >> Place Vendome >> Tuileries Gardens & Orangerie*
•Louvre Museum* (Closes 7.30pm)

Tuesday
•Sainte-Chapelle* (Opens 9am)
•Conciergerie*
•metro line 4 from Cite to Odeon, for Luxembourg Gardens
•metro line 12 from Notre Dame des Champs to Solferino for Musee d'Orsay* (Closes 6pm)
•Invalides* (Closes 9pm on Tue)

*sights included on Paris Museum Pass

I like David's plan, it focuses each day on a separate part of the city and takes advantage of museum hours. Don't get the Paris Pass, but consider the Paris Museum Pass, to save time and maybe money too. Use the website to compare the pass with individual admissions, and consider the value of avoiding ticket-buying lines (not as much of an issue in January as other seasons). The pass also lets you duck into other museums for a quick look or a single object, or a bathroom, without investing in the admission price.

Not sure what you want to see in Montparnasse, there's a good cemetery there and the iconically ugly Tour Montparnasse provides a bird's eye view of the city without the hassles of the Eiffel Tower. Otherwise it seems like it's out of your way.

A Seine cruise would be a good experience unless it's really bad weather. You can stay inside if it's too cold, though the views are better from the top deck. No reservation needed.

Yes, the top of the Montparnasse Tower is a great view of all of Paris and doesn't have the lines that the Eiffel tower has.
(the area is referred to as Montparnasse and there is the tall skyscraper (tower), a very large train station, several budget hotels in the area.)

Where are you staying? You arrive at Gare de L'Est, so it may be at least an hour to get to your hotel and check in. If your room isn't ready, you can leave your bags at the front desk.

A Paris Pass is a terrible deal. 2 EUR for 1 EUR of value. Get the 2-day Museum Pass and buy a 10-pac of transport tickets (a carnet) for less than 15 EUR and that should just about cover you for 2 1/2 days.
Everything else you want, go al la carte.

I do solo trips a lot and I'm not a particular fan of HOHO bus tours. I understand you are wanting to do it mostly to get your bearings upon arrival in a new city, but given your train gets in at noon, it's going to take you awhile to get to your hotel and ditch your bags, and you're visiting during the winter and it's going to get dark relatively early, you are going to be spending a good chunk of change on a bus ride as you're not going to extract much value from it by hopping on and off.

If you must do a bus ride to get your bearings, then maybe look at simply taking the lower cost option (without the commentary) and just get on the Route 69 or Route 42 bus. You can Google these routes to get information about the many sights you can see along these city bus routes at a fraction of the cost you'd pay for a HOHO.

While Montparnasse Tower can be a good alternative (especially in the winter when it's cold) to getting a 360 degree view of Paris without having to deal with the whole ticketing process of the Eiffel Tower, there are other places you can get a 360 degree view. You already want to go to the Arc de Triomphe - you can get a good view from the top of the Arc and the bonus is they are open until late at night so you could time it so you are on top of the Arc as the hourly light display kicks in for the Eiffel. If you are wanting a 360 degree view during daylight hours, then take the Route 42 bus and go to Galeries Lafayette Department Store and head for the Ice Cube Bar located on their rooftop terrace. If you can time it to be there just before sunset, even better - you can enjoy a drink with a view and still stay out of the cold and wind.

For the other 2 days, I'd get a Museum Pass so you can bypass ticket sales lines. You may even want to hold off on going to the Arc until you activate your Museum Pass as the admission would be covered. Personally, I love the Catacombs and apparently have been really lucky every time I have been as I've never encountered a horrendously long line there - not even when I went in peak summer tourist season. If it's something you really want to see, then I say play it by ear and see how the line is. Dress warm. It's a little chilly down there in the summer, so in January I'd expect even more chilly and damp conditions down there but as a result, I'd expect far fewer tourists and hopefully a shorter line to get in.

Another good view is on the top of Montmartre from the terrace in front of the Basilica. But January is gray and foggy, so again play it by ear. Otherwise, David has laid out a nice itinerary.

Thanks, all, for your advice and suggestions. Much appreciated.

Will get a 2 day Museum Pass and forget Montparnasse and the Catacombs. Thanks for layout itinerary, David!

I like bus public transportation and I'll look up the Route 69 or Route 42 bus instead of the HOHF bus.

I'm staying close to the Eiffel Tower, near Rue Cler.

For the transport tickets, I'm a little confused. Is it possible to transfer between two different lines? And for instance, I take a bus to the Louvre. Can I use that same ticket, within a certain amount of time, to take another bus route to the Arc? Or is that ticket done as soon as I get off the bus at the Louvre?

And since my train to London on Wednesday the 17th is at 8:40am, what time should I get to Gare du Nord? And it being that early, what's the best mode of transportation to get there? Metro? Or take a taxi?

Thanks again for your help!

If you are staying near Rue Cler, the 69 bus runs down Rue Saint-Dominique going toward, say the Louvre, then coming back it travels along the next street south, Rue de Grenelle toward the Eiffel Tower. I am pretty sure there is a bus stop on Rue Saint-Dominique just east of Rue Cler and right across from or near to ...gasp... Starbucks, lol!!

Have a wonderful time! Going solo in Paris is very easy and enjoyable.

You should be at Gare du Nord at least 1 hour before departure, as you will have to through security and UK immigration.

You arrive at Gare de L'Est. Easiest way is to take the No 7 Metro (direction Villejuif/Porte d'Ivry) to Opera and change to the No 8 Metro (direction Balard) and get off at Ecole Militaire.

Going to Gare du Nord, take the No 8 Metro from Ecole Militaire (direction Pointe du Lac) to Strasbourg-St Denis and change to the No 4 line (direction Porte de Clignancourt) and get off at Gare du Nord.

More info at https://www.ratp.fr/en/
route planners, maps, etc.

Transport tickets are time limited. They give about 1 hour to get from anywhere in Paris to anywhere else in Paris without stopping. Hold on to your ticket the whole time in case a fare inspector wants to see it. So to go to the Louvre on the bus, if you stop for any length of time, you'll need to use another ticket to continue on.

Subway and RER tickets are interchangeable with transfers; bus or streetcar is a separate fare.