The last census taken in Afghanistan was in the 70's. The UN and other humanitarian agencies have done surveys with gaps for “dangerous” areas. The finite answer is that no one knows how many Afghans there are let alone census quality demographic information.
Here is a typical study with the usual disclaimers: http:// measuredhs.com/pubs/pdf/FR248/ FR248.pdf
Taliban: Once again you hit a sore spot with the U.S. focus on the region. “Anti Government Forces” run the spectrum from foreign jihadis to squabbling political/tribal/ethnic factions.The taliban flow into regions evacuated by the US military and rapidly tax and press gang the population into a cohesive force. When special operations troops are present, their numbers are reduced. In the south there is a significant support and once again no hard numbers. We didn't count the Viet Cong in Viet-Nam, and we have failed to count the Taliban in Afghanistan. The short answer is “enough.”
This is as good as it gets with the same caveats for “dangerous” areas…the places the talibs thrive.