3. Is there a ban on corporate donations to political parties?

Political parties law: Article 15

http://www.iec.org.af/pdf/legalframework/law/politicalparties_law.pdf

There is no ban on corporate donations- however there is a limit of two million Afghani per year for all legal persons. 

Article 15: Political parties may receive income from the following sources: (b) Donations by legal persons up to two million Afghani per year.