The missile is developed based on the requirements of airforce. NG cannot be used in battlefield mobility, that's the role of QRSAM specifically designed based on army requirements.Can't comment on the numbers. But I do expect the Army will buy more NG than the IAF.
Unlike the AF which uses the missile in a static point defence role, Akash's battlefield mobility (a.k.a weight) has always been a major issue for the Army. Though they eventually settled for a truck-based launcher, they'd have preferred a T-72 or BMP-based one. DRDO demo'd both during trials but the Army wasn't quite happy.
They've wanted a lighter, more mobile, self-contained system for ages and NG promises just that.