There is no limitation regarding the validation of the German self-employment visa. Generally, the foreigner office will approve the resident permit for one year. After one year they will check if the business is running according to the expectations in the business plan and will extend the resident permit in this case. The performance of the business is important to extend the visa. If the business is not running well it is still possible to extend the resident permit, if you can explain the foreigner office the reasons for it.
