What wheels are you planning to use on this design? It looks like you'd be able to thin it down (and use less power while steering the modules) is you used Colson wheels... But switching your wheel choice means examining design priority: Do you want to push, or out maneuver? Crab makes a robot able to run circles around many other robots, but depending on ratios and wheel type, can also be a decent pushing bot.

I'd love to see the rest of your chassis for this design, it looks quite solid.