> arriving at 11:38 (track 1) and departing for Basel (track 9) at 11:48.

arriving at track 9, departing from track 4

> Can I get-off the train with luggage and walk from track 1 to 9 in less than 10 minutes?

Yes.

> If I have pre-purchased a ticket from Cochem to Basel, with a 10:59 departure, at a reduced fare of 39 euros, would I be allowed to board a earlier train at no change in fare, departing Cochem at 10:25 (arriving at 11:20) or one leaving at 9:59 (arriving at 10:35)?

10:25 train is possible, 09:59 train not.

The reduced fare tickets are only valid for the booked trains. This does however apply only for far distance trains booked (IC/EC or ICE trains). With regional trains you still have some flexibility. I.e. you can take 10:25 train.

The 09:59 train is an IC train and not covered by your ticket, as your ticket covers Cochem to Koblenz part only on regional trains.

> Is it possible to book and prepay on Bahn Db, using 2 trains with a greater connection time than the listed connections shown in the Bahn schedules?

You can select under "Ways: Duration of transfer" instead of standard "at least 15/30/45 minutes".

You can also "plan" stopovers. E.g. giving a via station with the length of the desired stopover. At max. 48 hours. The chance to get a reduced ticket will however decrease in most cases by doing so , as you need now 2 or more trains where the reduced fare tickets are not yet sold out (they are limited to a certain percentage of the seating capacity).

A 10 minute connection in Koblenz is doable.

Besides, according to my experience - I've been travelling the Rhine valley route quite often in recent times on the very same EC (11.14 from Bonn) - this train is almost always delayed, which gives you extra time. (Don't rely on that, though ;-))

Thank you so much for this very helpful information. I now feel much more comfortable with a 10 minute connection, although I may still try to take the 10:25 train - giving me another 30+ minutes in Koblenz. I would like to get a better look at the station and not have to run from train to train. Thanks again. Lori