greetings to Hasan and congretualtions for his positive result!
As you seem to be the virtual guide I kindly ask you to look for Wefugee community postings to get an answer to questions 2 and 4. If someone has new informatins to add this will surely happen. For an up-to-date estimation concerning question 2 see http://bit.ly/2aqnhp4
To answer question 3 see information of "Netzwerk Berlin hilft", section 1 "Asylberechtigung" http://bit.ly/2aql90U
Detalied information about Act on the Residence, Economic Activity and Integration of Foreigners in the Federal Territory Residence Act see http://tinyurl.com/j4dr5rk
. Maybe you had practical outcome of the positive answer of BAMF in mind, then tell us something about what you would like to do.
Concerning question 1 I would advise you to review your first choice. Frankfurt may be the beneficiary of Brexit, many financial institutions think about leaving London and will probably move to Frankfurt, subsequently cost of living and rental fees may rise in cost.
Kind regards, Jan