Question 1: I could just find that these fares are only valid on said train and date. No other information. By calling DB, they told me that in case of delay, you'd automatically would be entitled to hop onto another train. In case of early arrival, no possibility to get an earlier train.

Question 2: There is sufficient stowage space overhead and otherwise a special luggage rack close to the doors: In this case, just keep an eye on your luggage at in-between stops.
Have a good trip.