If you want to use a job ad in your search for staff members, you have to be aware of the fact that you cannot include everything you want in the text. For instance, an age limit or a preference for gender of the applicant shall be deemed to be discrimination; exemptions apply to exceptional cases only.
Before inviting applicants for an interview, you will probably search the internet or social media for names. Such a screening may violate the applicants’ right to privacy and is therefore not allowed just like that. This is not the case if they have given unambiguous consent for the screening. You can ask for this consent, for instance, by requesting to tick a box on your website or by mentioning in your job ad that internet research will be part of the application procedure and will require the consent of the applicant.
Once you have found the perfect candidate, it is crucial that a clear employment contract in writing will be agreed upon at the time of appointment.