Also use bahn.de for Colmar to Staufen. Best (infrequent) route; Colmar to Basel, onto Bad Krozingen, bus or train from Bad Krozingen to Staufen. Konus covers Basel to Staufen. ICE trains not covered.
If you haven't booked accommodations yet, Staufen and Freiburg can both be reached easily from Gengenbach. You can spend a day in Freiburg. If you fancy a pleasant, easy stroll, you can make a day of Staufen: get off at Bad Krozingen, walk along the creek which leads to Staufen (about an hour) and further to Munstertal.
The long train ride to Freiburg via Donaueschingen (change) is supposed to be scenic.
Direct train from Gengenbach to Konstanz. Konus covers most of it.