I love having fewer clothes. It makes everything easier. Really you don't need much more than a laundry cycle's worth of clothes.
For maternity, I have enough to make it through the weeks laundry cycle. So jeans, yoga pants, long and short sleeve t-shirts, a few pullover sweaters and a few dresses and a pair of leggings for church/when nothing else fits. I bought a maternity robe this time and am really loving it.
I agree with purging as you grow. I would also think about getting rid of everything at the bottom of your drawers/back of your closet. The things you always pass over. I wear my regular knickers and tank tops throughout pregnancy, so find time to sort those too.
When you start buying new clothes, come up with a plan first so you don't end up with too many extras.