Sure, you can perfectly make those journeys with your pass. You wil need a reservation for TGV 9580. There are limited seats for passholders in this train and they often sell out a number of days in advance, so don't leave it too long. Although there are also reservation-free alternatives, by using the frequent regional train to cross the border to Strasbourg.

You can indeed save a bundle (probably >30€!) by simply using ONLY INland fast trains in CZ and DE-these are only with optional REServation (If wanted, can be done for just 4€ via bahn.de, click on seat-only, though I think the train from Praha itself does not even offer RES).

For most trains the last stop In DE is Offenburg, maybe Karsruhe. From Ofb use the hourly local regional shuttle to Strassburg/Strasbourg. It will lengthen the trip with maybe 20/30 mins and involve 1 extra change.