Well, since crystalblend will be able to compile and run the models and maps in Blender, then yes, won't hurt to know it. Cubes can be duplicate quickly and the snap to grid option should take care of the seams.
If you want to make sure about the size, you could try importing a room into max or blender and use the grid as a guied
There are many of games that is made with crystalspace and can be download, look at the project page for a listing, PlaneShift is the most active at this moment, fuel is a commercial game, I think Bronz is too
http://www.crystalspace3d.com/tikiwiki/tiki-directory_browse.php?parent=1