How many minor languages are spoken in Afghanistan? What are the positives and negatives to such linguistic and culture variance?

I will try to answer only on the first question of yours. Minor languages may include Hindi-Urdu, Punjabi, Ashkunu, Kamkata-viri, Vasi-vari, Tregami and Kalasha-ala, Pamiri (Shughni, Munji, Ishkashimi and Wakhi), Brahui, Arabic, Qizilbash, Aimaq, and Pashai and Kyrgyz. Linguist Harald Haarmann believes that Afghanistan is home to more than 40 minor languages, with around 200 different dialects.