once a person has lived in Germany for four years, the authorisation of the Employment Agency is no longer required as a rule. For more information see information of the German Federal Office for Migration and Refugees BAMF: http://tinyurl.com/jzsmwd7
To become a naturalized citizen, you have to have lived in Germany under a limited residence permit for at least eight years.
See a brief summary of conditions, provided by 'justlanded.com': http://tinyurl.com/lcsld4s
The "Zertifikat Integrationskurs" can help you with naturalisation. You may apply for German citizenship after seven years of lawful residence in Germany if you have been awarded this certificate. The usual requirement is eight years. (BAMF: http://tinyurl.com/k9tdddu
For more details see information of 'the local.de - Germany's news in English': http://tinyurl.com/ll9rj5p