European Road Trip Munich to Paris

I assume you are OK with the international fee for dropping German hired car in Paris and included that in your calculations. Don't forget an International Drivers Permit need the need to buy vignette stickers for Czechia, Austria, and Switzerland.

Thank you, that he is included in the rental. They also mentioned cross border fee, not sure about the vignette stickers, is that the same thing? Where world we buy those?

You can buy these at fuel stations at the border. Czechia and Austria have 10-day versions, Switzerland is annual only. Not big budget items (10 to 20 EUR for CZ and AT, 40 CHF for CH), but fines are hefty if you forget.

There are direct trains from Munich to Prague (5h 45m). I can see renting a car for hard to get to places by public transportation but not for places that are easier by taking the train: https://int.bahn.de/en. Pick up the car in Prague instead of Munich.
Austria, Liechtenstein and Switzerland are outliers so remove those countries from your itinerary.
Are you spending time in Paris or dropping off your car when you get there and flying home the next day? It’s best to allow five nights in Paris. Instead, drop off your car in Reims and take a direct train to Paris (1h): https://www.sncf-connect.com/en-en/.
Sometimes the ambience is missed when we don’t spend enough time in a place. Slow down and enjoy your time there. Driving on the opposite side of the road in a car you’re not use to then finding a place to park is not fun.

Sometimes the ambience is missed when we don’t spend enough time in a place. Slow down and enjoy your time there. Driving on the opposite side of the road in a car you’re not use to then finding a place to park is not fun.

I agree about missing the ambience and it is good to slow down. I'm not sure where Diane is from. If she is from the US, there's no place they will be where they will drive on the opposite side of the road.

I'd feed that entire route into ViaMichelin.com to get an estimated driving time. That won't include any stops, traffic tie-ups, looking for parking, etc., but it may be a reality check. Five countries (I'm not counting Liechtenstein) in 17 nights is a lot. Whether it's at all reasonable for you depends, I think, on how many cities you actually intend to visit. You mentioned Prague, which needs at least 3 nights (I'd recommend more; it's gorgeous). What about Vienna? Salzburg? Swiss cities (March not seeming a great time for the Alps unless you're into winter sports)? French cities? Do you plan to spend a few days seeing Lake Constance--though I'm not sure what the gardens will be like in March. Seventeen days would be a lot of time for me to look at scenery through the windshield, and the weather could be chilly and wet at that time of year. I'd be planning considerable time in cities, myself, and I'd want enough time to enjoy what they have to offer.

rental. They also mentioned cross border fee, not sure about the vignette stickers, is that the same thing? Where world we buy those?

Any cross border fee will be a charge made by the car hire company for going outside the boundaries of the country where the car was hired. That will be in addition to the very high drop charge for leaving the car in a country not where it was hired - often between 600€ and 1000€ or more depending entirely on the company policies.

The Vignette is for usage of toll roads in specific countries, issued by those countries (Czech Republic, Austria, Slovenia, Switzerland - all except Switzerland have a short term one of around 10€, the Swiss one is an annual one, most recently CHF40) instead of collecting tolls on highways. Once the sticker is affixed correctly on the windscreen it can be driven on any amount of toll motorways in that country for the specified period for no additional charge... except Austria which also has tolls payable on several highways and a very long tunnel. Those additional tolls are paid in cash or card at a tollbooth in the traditional way.

Germany has no tolls for passenger cars but it does for freight wagons. Italy has toll motorways and so does France, very expensive ones.

Vignettes are usually purchased at fuel stations on the highway or sometimes in border towns at petrol stations, or at the border control.

Fines for not having them or not displaying then correctly, are very steep.

I hope that that clears up that question a bit.

MaryPat, thanks for the advice. I did try to hire the car from Prague but unfortunately that was not as easy as it sounded. So we thought we would use the car outside Munich to see the castle etc, and then continue on to Prague. I figured we would be passing through Austria, say Salzburg, easily on the way back to the Black Forest, and from there down to the outskirts of Switzerland and into France. Liechtenstein is only 25km long, and we thought we could just pass through on the way up to Lake Constance in order to say we've been there :).

I'm aware that some of the alpine passes will still be closed at this time of year, so we'll be constrained as to our route by that.
I'll look into your advice on leaving the car in Reims, we had intended to drive into Paris and drop it off there and spend the time in Paris on foot or public transport.

Thank you @Nigel, that's great advice.

regarding taking the car into Paris (or other larger French towns and cities) - it is worth knowing that cars which are not registered in France are unlikely to come with a Crit'Air windscreen sticker. https://www.rac.co.uk/drive/news/motoring-news/law-change-for-uk-drivers-in-french-cities/ This sticker allows you to drive into environmental control areas, such as Reims, Strasbourg and Paris among several others. Without it you are liable to a large fine. Advice for driving a non French car towards a large city is to park on the outskirts - which may be further out than you expect, or travel by train. https://www.ecologie.gouv.fr/sites/default/files/QA-critair_flyer%20EN.pdf

Since you will have a German hired car it will have the German required Umweltplakette, so no worries there.

An idea to save costs. You could rent the car in Munich, drive to Prague and back via Austria, Switzerland, Alsace region and Black Forest and return the car in Germany at the border to France (e.g. Freiburg or Karlsruhe). I assume that this would make the rental cheaper.
From there you can take the train or rent a car again in France (this also would solve the Crit'Air sticker problem).

For preparation: The following website (in German only, so activate translation in your browser) has summarized the toll and environmental zone rules of most European countries.
https://www.adac.de/reise-freizeit/maut-vignette/

The toll stickers are now also available online, but you must already know the license plate number. Here are the links.
Czech Republic: https://edalnice.cz/en/map-of-toll-roads/index.html#/road_map
Austria: https://www.asfinag.at/en/toll/
Switzerland: https://via.admin.ch/shop/dashboard
Buying them at the border or at a petrol station near the border is probably easier.