In addition to the already given info: Not in Luxembourg but certainly worth to consider about ‘The Battle of the Bulge’ is Bastogne, more info see: www.bastogne-tourisme.be (select English). I have no experience with guided tours, but according Tripadvisor ‘Battle of the Bulge Guided Tours’ and ‘Reg Jans Battlefield Experience - Day Tours’ are highly recommended there.
You can visit the well-known Mardasson Memorial just outside town with the nearby new Bastogne War Museum. Bastogne Barracks is certainly worth to consider, where you can visit during the week the ‘Vehicle Restoration Centre’. However the Belgian Government has plans to close the latter, so check out if it´s still open to public.
In Luxembourg there are several smaller museums about the battle like those in Diekirch and Ettelbrück.
To my opinion you need more than one day to see everything well.
From Brussels a daytrip to Luxembourg is doable with a rentaI car if you like to see different places, public transport will in this case too much of a hassle.