Besides that, trust me, it is a major pain to write SW to control 4 individually steered modules.
I suggest anyone doing crab/swerve should steer at least two wheels together with each globe motor. Either the fronts and backs together, or the sides together, depending on what type of flexibility you need for your driving strategy. For example, in 2008, having the two fronts tied together and the two backs tied together allowed what we call monster truck steering easily around the tight hairpin turns.
Last year, 2009, we tied all 4 together for the first time since the low traction surface made it moot to control them separately.