Why was a Special Counsel appointed to investigate "Russia Collusion?

I ask this question for 5 reasons:

• The Dossier was known by DOJ and FBI to be unverified and outlandish claims paid for by Hillary Clinton's campaign
• Nothing in Jim Comey's "Memos" that were leaked to trigger the appointment of a Special Counsel support the obstruction of justice claim in the media
• Why so fast? Compare the decision time to appoint a Special Counsel compared to the months of pondering if their should be a Special Counsel to investigate Hillary Clinton's various issues.
• Why Robert Mueller? His close relationships and friendships with many of the players involved surely should have disqualified him?
• Why did Rod Rosenstein have to recuse himself if the same standards were applied as they were to Jeff Sessions. Remember Rosenstein signed one of the FISA warrants and oversaw the UraniumOne investigation?

Just as importantly - now we know there was no collusion or obstruction by the President - why has the Special Counsel handed off the prosecutions for "wrongdoing" they claim to have found to DOJ and shut themselves down?