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For permanent residence and the operation of a company, you need a settlement permit for Germany.
Prerequisites are 5 years staying in Germany, knowledge of German language, secure income, 60 month payment into the pension, cf. § 9 AufenthG
Easy conditions are, because you have a child in Germany, 3 years residence in Germany, simple knowledge of German and there is no proof to the pension. However, the living must be secured without social security benefits.
You write that you have a Schengen visa for four years. If this is a so-called long-term resident-EG visa, syou can change in a long term in Germany-Visa. Also, you could request a national permanent residence visa on the basis of this visa.
However, do you have a permanent residence visa for an another EU country, you can request a permanent residence for Germany. You must demonstrate that you have a sufficient health insurance coverage (you have) and secure your livelihood. you must also specify and that you will do your own business and show that you have the financial power to do that.
Your non-existent knowledge of German Language represent the biggest obstacle at the moment. You must prove that knowlegde at the moment you ask for the permant redsidence.
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Anja Merkel, LL.M.