About the Box
Options / Units System/ Millimeters :)
Draw Solid / Box 3 points and enter your measures :)

About triangulation : you have several choices when you export an object in OBJ format :)
Ngons, Quad & triangles, Only triangles and inside some regulates can be made :)
see this doc http://moi3d.com/1.0/docs/moi_command_reference10.htm#meshdialog