Hi @Smart Djaba
Generally it is not the duration of the permit but rather the type of permit which decides whether a person can set up a company. I’m not sure on the classification of a gUG but if it is categorised as self-employment, then with a three year permit you are likely to be allowed to do so. If your permit has something like ‘Erwerbstätigkeit erlaubt/ gestatt’ written on it (or on the paper 'Zusatzblatt' that comes with it) then it means you can be self-employed.
You can work as an employee while setting up a company. Generally you should speak to your employer about this so that they are ok with it. You will also have to do a tax declaration.
There are a range of supports available to migrants who wish to start a business. This ranges from the states supports offered by the Agentur für Arbeit and Jobcenter to specific projects set up to assist and advise throughout the process. If you search for something like ‘Existenzgründung’ and ‘Migrant’ in your area you may find such a project.
This site provides extensive information and resources:
https://***.existenzgruender.de/EN/Home/inhalt.html
This is a useful handbook in English:
https://cdn.kettufy.io/gp.kettufy.io/documents/gruenderplattform.de/2022_Leitfaden_Einfach_gruenden_in_Deutschland.pdf
The information applies to migrants wishing to set up a business. I am not aware to what extent they assist in the case of a gUG as it is a type of non-profit business as I understand it. For help with a gUG, it may be better to speak to someone who helps migrants set up non-profit organisations such as a ‘Verein’.
Best,
Éanna