Absolutely! Germany is wonderful for travel and sightseeing. Here are some tips for your visit to Stuttgart, Mannheim, and Heilbronn:

Best Time to Visit:
The best time to visit these cities in Germany would be from late spring to early autumn (May through September) when the weather is warm and pleasant for sightseeing. However, do keep in mind that summer months can get quite busy due to the tourist high season.

Route and Accessibility:
All three cities are well connected by Germany's efficient train system. You can easily reach Stuttgart from Frankfurt or Munich in 1-2 hours by ICE (InterCity Express) train. Regular trains are also available from Stuttgart to Mannheim (about 38 minutes) and Heilbronn (about 37 minutes).

Altitude and Acclimatization:
The cities are located at relatively low altitudes, so there should not be issues related to acclimatization or altitude sickness.

Accommodation and Booking:
There is a wide range of accommodations available in these cities including hotels, guesthouses and serviced apartments. It's recommended to make your booking in advance especially if you plan to travel during the peak tourist season.

Clothing and Essentials:
As the weather in these cities can be quite variable, it's advisable to carry a mix of clothing suitable for both warm and cold weather. Don’t forget your comfortable walking shoes as these cities offer several sightseeing opportunities.

Health and Safety:
Public health and safety standards are high in Germany. However, it's always helpful to carry a basic first-aid kit including any medication you may need. Also, maintain the usual caution regarding your personal belongings.

Local Etiquette and Respect:
Germans are known for their punctuality and etiquette, so try to be on time for any appointments. While visiting any religious or cultural sites, be respectful to the local traditions and customs. Also, learning a few basic German phrases can prove very helpful during your trip.