I have never had tickets mailed, although I have heard of people having success with this method. I have purchased tickets for "self-printing", and that worked well.
As for connection time, 10-15 minutes should be plenty of time. Check the schedule on the German Rail website to see what the tracks of the connecting trains are. I see one connection in Mannheim from track 3 to track 5 in 15 minutes. That would be easy to make. The 9 minute connection in Stuttgart from track 6 to track 16 would require you to move quickly, but not run.
Remember, a lot of people will be making this connection. If the train from Paris is late, they will probably hold the train to Munich. If not, there is another train in a hour, and your tickets will be valid on it.
The important thing to remember when making any train change is to be prepared.
Know the number of your connecting train's platform.
A few minutes before the train comes into the station, get up, get your thing together, and move to the end of the car. When the train stop, get off. The people waiting to get on will wait for you to get off.
Proceed without hestitation to the connecting platform. There will be clear signs. In Mannheim you will have to go down steps to a tunnel between the tracks. The number of the tracks will be clearly displayed next to the steps in the tunnel. Stuttgart is a "dead end" station. You will have to walk along the platform to the front of the train, then along the connecting platform to track 16.
