In terms of macro-level countering, not a whole lot...
But you have to realize that Machine Guns are a defensive unit, not an aggressive unit per se.
Your weakness will be artillery, because the Howitzers will work well against your Infantry (Machine Guns), and since your Tanks will most likely be out in front battling his other Tanks in his front of his army, the Howitzers in the back will be protected in the back (most likely) and will try to fire on ur inf...
In terms of micromanagement, your Machine Gunners are slow and fixed on one position, so they are extremely vulnerable to flanks. Your strategy basically relies on the Tanks surviving the initial battle as your Machine Guns get close onto the enemy Infantry. If your opponent knows how to Flank with Tanks, then you'll have a hard time recovering.
My advice: Well, Number one, always have an eclectic army... that means having a multitude of types in your army so your not reliant on 1 or 2 unit types. That being said, if you would like to continue with your strategy, make sure you have a LOT of air power to compensate for your lack of movement speed with regards to your army as a whole.
Pimp approved, master class!