Hello njxbean, if you drive directly from Frankfurt to Stuttgart, it will take you approx. 2 hours on the Autobahn *if* there is no traffic. (Which is generally the case on Sunday at 3 o'clock in the morning...) I prefer the train, which take 70 minutes from Frankfurt to Stuttgart: on the first half of the trip, the train runs at 160 km/h, while on the second half, it travels 250 km/h. Even if you rent a Porsche, you won't equal that.

I would only take a car if you want to do sightseeing on the way, either visiting castles or visiting wineries. If that's your wish, let me know and I'll make some suggestions. But if you just want to get to Stuttgart, take the train.Yes, you can buy a ticket on the spot, at the airport and at the main station. There are also ticket machines, which offer English as well as German. You can generally pay the machines with a credit card or cash. If you buy a flexible ticket from Frankfurt Airport to Stuttgart, it will cost you € 61.10 in 2nd class and € 103.20 in 1st class. 2nd class is good enough on the ICE trains! 1st class is only worth it if you are traveling at a peak time like Friday afternoon. Just by the way, though, if you book a ticket in advance for a particular train, you can save a lot of money. For example, I just put in Aug. 4th as a date, and www.bahn.de shows many ICE trains for € 17.90 in 2nd class and € 26.90 in 1st class. You can buy the ticket on the web site and just print it out at home. It could be worth buying a fixed ticket and taking the risk you lose it! None: You will have to wear a mask in the train.

The rules for wearing masks are changing constantly. As of today, restaurants in Stuttgart are allowed to be open normally and to serve you inside and outside with no masks required. However, if the number of new COVID cases were to rise above 35 for more than 5 days in a row, the restrictions would be put in place again. It is really not possible to forecast how it will be on a specific date in August! But on the other side, restaurants will be allowed to serve outside even if the number of cases goes up sharply, and August is a usually good month for eating outside! They might then require a Corona test, but these are generally available for free or cheap (like € 2.00), so that shouldn't hinder you.

I just checked Frankfurt's web page for Corona restrictions. They seem to currently have more requirements for wearing masks, but everything is open, And again, 5 weeks is a long time right now. It's really not possible to say how it things will be then!

Have a good time in Germany!