Question 1: see information of BAMF: http://bit.ly/29qMf6R
More details by Handelskammer Hamburg, in German: http://bit.ly/29qNfrJ
But things seem to change, see newspaper article here: http://bit.ly/29qN53R
Question 2: To give a generalizing answer: I found no confirmation for a total tax exemption.
You surely can save a lot of money as a business start-up freelancer, but this is depending on many conditions and details. Ask a professional tax accountant, this matter seems in permanent move to me.
Short information (in German): http://bit.ly/29qPJGC
Detailed information by Handelskammer Hamburg (in German): http://bit.ly/29qPiMl
Question 3: You need a "Gewerbeschein", make a request at your local "Gewerbeamt"
Details in German: http://bit.ly/29qQC20
Kind regards, Jan