Having gone down that way a couple of times I would go a slightly longer route but cheaper!
Go to Gent, Brusselles, Namur,and down through the Ardennes to Luxembourg, then Saarbrucken, all of which is on free motorways of very good quality. You also get the advantage of cheap fuel in the Ardennes and Luxembourg.
Thereafter a good selection, but consider down to Strasbourg, then down the (free) autoroute to Colmar.
Although Colmar is nice enough, have you considered Obernai? Beautiful old quaint town with (we think) one of the best municipal sites in France. From there you can do Colmar, Strasbourg, the only Concentration Camp in France, and Le Ligne. Offenbourg and Freibourg are only just across the Rhine.