Pakistan needs more people. People are your assets as long as they are educated. With Pakistan's growing economy, the more people can benefit from it and benefit the country as well. I am not saying that you be like the Chinese or the Indians. But I think 300 million in the next 15-20 years would give you one of the largest population sizes, as well as the economy will respectively grow as you'll need to build buildings, homes, clothing, schools for these additional people. And if educated, this massive pool of people can then be provided to other countries as labor. Just like India did.
Both India and China have grown primarily due to their population size. If you are so heavily population, your internal economy will remain strong as you'd have to provide for your population. So, how much business you do outside, means less. So a heavy population means your internal businesses keep running to provide for your own population, and the consumers keep buying so your economy always remains stable and grows as new generations come. I'd say 2-3 children are a must per family.